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^CHEMISTRY 

OF 

FOOD  AND  NUTRITION  . 


BY 


HENRY   C.    SHERMAN,    Ph.D. 

PROFESSOR   IN   COLUMBIA   UNIVERSITY 


SECOND  EDITION 
REWRITTEN  AND  ENLARGED 


THE   MACMILLAN   COMPANY 

1918 

Ali  rights  reserved 


I 


4^\ 


^^w 

.% 


x^^ 


Copyright,  191 1  and  191 8, 
By  the  MACMILLAN  COMPANY, 


Set  up  and  electrotyped.     Published  February,  1911. 
Second  Edition,  Rewritten  and  Enlarged,  March,  1918. 


Nortoooli  i3ress8 

J.  S.  Cashing  Co.  —  Berwick  &  Smith  Co. 

Norwood,  Mass.,  U.S.A. 


PREFACE 

The  purpose  of  this  book  is  to  present  the  principles  of  the 
chemistry  of  food  and  nutrition  with  special  reference  to  the 
food  requirements  of  man  and  the  considerations  which  should 
underlie  our  judgment  of  the  nutritive  values  of  foods.  Food 
is  here  considered  chiefly  in  its  relations  to  nutrition,  the  more 
detailed  description  of  individual  articles  of  food  and  the  chemi- 
cal and  legal  control  of  the  food  industry  having  been  treated 
in  another  volume. 

The  present  work  is  the  outgrowth  of  several  years'  experience 
in  teaching  the  subject  and  is  published  primarily  to  meet  the 
needs  of  college  classes.  It  is  hoped  that  the  book  may  also 
be  of  service  to  other  readers  who  appreciate  the  importance  of 
food  and  nutrition  as  factors  in  health  and  are  interested  in  the 
scientific  foundations  which  have  been  so  greatly  broadened 
and  strengthened  by  the  investigations  of  the  past  few  years. 

While  the  small  size,  to  which  the  book  is  limited  by  its  main 
purpose,  permits  little  of  either  historical  or  technically  critical 
treatment,  yet  a  limited  number  of  original  investigations  and 
of  controverted  views  have  been  discussed  in  order  to  give  an 
idea  of  the  nature  of  the  evidence  on  which  our  present  beliefs 
are  based,  and  in  some  cases  to  put  the  reader  on  guard  against 
theories  which,  while  now  outgrown,  are  still  sometimes  en- 
countered. 

Special  attention  has  been  given  to  the  difficult  task  of  at- 
tempting to  present  the  striking  results  of  some  of  the  most 
recent  investigations  in  nutrition  in  such  a  manner  as  to  make 
clear  their  importance  without  giving  exaggerated  impressions 
and  with  due  emphasis  upon  the  fact  that  on  many  significant 

V 


VI  PREFACE 

points  any  interpretation  which  can  now  be  offered  is  necessarily 
tentative.  It  is  hoped  that  study  of  the  text  will  be  supple- 
mented by  consultation  of  the  references  suggested  at  the  close 
of  each  chapter,  which  should  serve  to  put  the  reader  in  touch 
with  much  of  the  more  significant  Hterature  and  make  him 
familiar  with  the  scientific  journals  in  which  the  future  develop- 
ments of  this  rapidly  growing  subject  may  be  followed  as  they 
appear. 

The  author  desires  to  express  his  indebtedness  to  the  col- 
leagues and  former  students  who  have  contributed  many  helpful 
suggestions  and  specifically  to  Doctors  A.  W.  Thomas  and  M.  S. 
Rose,  Miss  L.  H.  Gillett  and  Miss  H.  M.  Pope  for  valuable 
criticism  and  assistance  in  the  preparation  of  the  present  re- 
vision of  the  work. 

H.  C.  S. 

November,  19 17. 


CONTENTS 


PAGE 

Introduction .        .      xi 


CHAPTER  I 

Carbohydrates i 

Classification.  Properties  of  the  chief  carbohydrates  of  food. 
References. 

CHAPTER  II 

Fats  and  Lipoids 19 

Fatty  acids.  Simple  and  mixed  triglycerides.  Formation  and 
composition  of  natural  fats.  Storage  of  fat  in  the  body.  Fats  and 
lipoids  as  body  constituents.     References. 

CHAPTER  III 

Proteins 42 

Chemical  nature  and  physical  properties  of  proteins  in  general. 
Classification.  Properties  of  some  individual  proteins.  Relation 
between  chemical  constitution  of  the  proteins  and  their  food  value. 
References. 

CHAPTER  IV 

Enzymes  and  Digestion 69 

Classification  and  general  properties  of  enzymes.  Activity  of 
the  digestive  enzymes.  Salivary  and  gastric  digestion.  Intes- 
tinal digestion.  Bacterial  action  in  the  digestive  tract.  Coeffi- 
cients of  digestibility  of  food.     References. 

CHAPTER  V 

The  Fate  of  the  Foodstuffs  in  Metabolism       ....    104 
Carbohydrate.     Oxidation  of  carbohydrate.     Production  of  fat 
from  carbohydrate.     Fat.     Oxidation  of  fat.     Storage  of  food  fat 


Viii  CONTENTS 


in  the  body.  Can  carbyhodrate  be  formed  from  fat?  Proteins. 
Absorption  and  distribution  of  protein  digestion  products.  Utili- 
zation of  protein  in  the  tissues.  Formation  of  carbohydrate  from 
protein.  Production  of  fat  from  protein.  Fate  of  the  nitrogen  in 
protein  metabolism.    References. 

CHAPTER  VI 

The  Fuel  Value  of  Food  and  the  Energy  Requirement  of  the 

Body 138 

Heats  of  combustion  of  the  foodstuffs.  The  physiological  fuel 
values  of  food  materials.  Table  of  loo-Calorie  portions.  Energy 
requirements  in  metabolism.  Methods  of  study  and  amounts  re- 
quired for  maintenance  at  rest.     References. 

CHAPTER  VII 

Conditions  Governing  Energy  Metabolism  and  Total  Food  Re- 
quirement   170 

Basal  metabolism  of  the  adult.  Influence  of  muscular  work. 
Influence  of  food.  Regulation  of  body  temperature.  Influence 
of  age  and  growth.     References. 

CHAPTER  VIII 

Factors  Determining  the  Protein  Requirement  .  .  .  203 
Protein  metabolism  in  fasting.  Nitrogen  balance  experiments 
and  the  tendency  toward  equilibrium  at  different  levels  of  protein 
intake.  Protein  sparing  action  of  carbohydrates  and  fats.  Pro- 
tein requirement  in  normal  nutrition.  Difference  between  mini-, 
mum  requirement  and  standard  allowance  of  protein.  Influence 
of  the  choice  of  food.  Influence  of  muscular  exercise.  Protein 
requirement  in  relation  to  age  and  growth.    References. 

CHAPTER  IX 

Inorganic  Foodstuffs  and  the  Mineral  Metabolism         .        .    234 
The   elementary   composition   of   the   body.     Metabolism   of 
chlorides.    Use  of  common  salt.    Metabolism  of  sulphur.    Me- 


CONTENTS  IX 

PAGE 

tabolism  of  phosphorus.  Interrelations  of  phosphates,  phospho- 
proteins,  and  phosphatids.  Estimation  of  the  phosphorus  re- 
quirement. Phosphorus  metabohsm  with  different  amounts  of 
phosphorus  in  the  food.  Phosphorus  in  food  materials  and 
typical  dietaries.     References. 

CHAPTER  X 

Inorganic  Foodstuffs  and  the  Mineral  Metabolism  (continued)  260 
Metabolism  of  sodium,  potassium,  calcium,  magnesium.  The 
calcium  requirement.  Calcium  content  of  typical  foods.  '  Re- 
lations of  the  inorganic  elements  to  each  other.  Inorganic  ele- 
ments in  American  dietaries.  Output  of  inorganic  elements 
during  fasting.  The  maintenance  of  neutraUty  in  the  body. 
References. 

CHAPTER  XI 

Iron  in  Food  and  its  Functions  in  Nutrition    ....    285 
Development  of  modern  views.    The  iron  requirement  of  the 
body.    Iron  in  foods.     References. 

CHAPTER  XII 

Antiscorbutic  and  Antineuritic  Properties  of  Food  .  .310 
Unidentified  essentials  in  food.  Scurvy  and  the  antiscorbutic 
property  of  food.  Infantile  scurvy  (Barlow's  disease).  Anti- 
neuritic properties  of  food.  Attempts  to  isolate  an  antineuritic 
substance.  Relation  of  chemical  structure  to  antineuritic  action. 
References. 

.    CHAPTER  XIII 

Food  in  Relation  to  Growth  and  Development         .        .        -331 
Nutritive  requirements  of  the  growing  organism.     Growth  pro- 
moting substances  in  food.     Influence  of  restricted  food  supply. 
Dietary  deficiencies  of  individual  articles  of  food.     References. 

CHAPTER  XIV 

Dietary  Standards  and  the  Economic  Use  of  Food  .        .    360 

The  general  problem  of  a  dietary  standard.     Energy  allowances 
for  adults.    Energy  allowances  for  Qhildreo.    The  problem  of  a, 


X  CONTENTS 

PAGE 

Standard  for  protein.  Opinions  regarding  the  value  of  liberal 
protein  diet.  Protein  standards  for  children  and  for  family 
dietaries.  Standards  for  the  calcium,  phosphorus,  and  iron  con- 
tent of  the  dietary.  The  unidentified  essentials.  The  economic 
use  of  food.    References. 

APPENDIX  A 

Nomenclature  and  Classification  of  the  Proteins   .        .        .    403 

APPENDIX  B 

Composition  of  Foods 407 

Explanation  of  tables.  Edible  organic  nutrients  and  fuel  values 
of  foods.  Ash  constituents  of  foods  in  percentage  of  the  edible 
portion.  Protein,  calcium,  phosphorus,  and  iron  in  grams  per 
100  Calories  of  food  material. 


INTRODUCTION 

The  activities  on  which  the  life  of  the  body  depends  involve 
a  continuous  expenditure  of  energy  and  a  constant  exchange  of 
material.  Ultimately  the  body  is  dependent  upon  food  for  the 
fuel  materials  which  supply  energy  and  for  both  the  substances 
which  are  transformed  in,  and  eliminated  from,  the  body,  and 
those  whose  presence  regulates  and  controls  these  transforma- 
tions. The  materials  leaving  the  body  are  to  be  regarded  not 
merely  as  wastes  but  as  end  products  of  an  orderly  and  co- 
ordinated series  of  chemical  reactions  which  occur  in  the  body 
and  by  virtue  of  which  its  functions  are  performed.  Thus  the 
chief  functions  of  food  are:  (i)  to  yield  energy,  (2)  to  build 
tissue,  (3)  to  regulate  body  processes. 

These  functions  involve  reactions  which  are  dependent  upon 
the  chemical  composition  and  constitution  of  the  food.  Any 
food  constituent  which  takes  part  in  any  of  these  functions  may 
be  regarded  as  having  nutritive  value. 

Most  of  the  nutrient  material  contained  in  food  requires 
more  or  less  change  to  bring  it  into  the  exact  forms  most  useful 
in  nutrition.  These  changes  as  a  rule  take  place  in  the  digestive 
tract  and  together  constitute  the  process  of  digestion. 

The  changes  which  take  place  in  the  foodstuffs,  after  they 
have  been  absorbed  from  the  digestive  tract,  are  included  under 
the  general  term  "metabolism."  Although  the  chemical' 
changes  and  the  energy  transformations  are  of  course  insepa- 
rable, it  has  become  customary  to  speak  of  the  metabolism  of 
matter  and  the  metabolism  of  energy,  and  to  regard  the  extent 
of  the  metaboHsm  of  any  material  substance  as  measured  by 
the  amount  of  its  end  products  eliminated,  and  the  extent  of 


XU  INTRODUCTION 

the  energy  metabolism  as  measured  by  the  amount  of  heat,  or 
of  heat  and  external  muscular  work,  which  the  body  gives  off. 

The  metaboHsm  of  matter  and  the  metabolism  of  energy  are 
normally  supported  by  the  food ;  but  if  no  food  is  taken,  they 
continue  at  the  expense  of  the  body  substance.  The  expendi- 
ture of  energy  can  never  cease  in  the  hving  body  because  it  in- 
cludes the  work  involved  in  carrying  on  the  internal  processes 
which  are  essential  to  life  itself ;  and  the  expenditure  of  matter 
cannot  cease  because  the  energy  for  this  necessary  work  is  ob- 
tained by  the  breaking  down  of  the  organic  compounds  of  the 
food  or  of  the  body  substance  into  simpler  compounds,  many  of 
which  are  of  no  further  use  to  the  body  and  must  be  eliminated. 
When  the  food  supphes  sufficient  energy,  the  body  substance  is 
protected;  when  the  food  is  insufficient,  body  substance  is 
burned  as  fuel.  In  order,  then,  to  consider  intelligently  the 
nutritive  requirements  of  the  body  as  regards  the  substances 
of  which  it  is  composed,  it  is  necessary  first  to  know  whether 
the  fuel  requirements  (the  requirements  of  the  energy  metab- 
olism) have  been  fully  met. 

The  carbohydrates,  fats,  and  proteins  of  the  food  all  serve 
as  fuel  to  yield  the  energy  required  for  the  activities  of  the  body, 
and  the  proteins  serve  also  as  material  for  the  maintenance  or 
growth  of  body  tissue.  But  of  the  fifteen  chemical  elements 
which  are  essential  to  the  structure  and  functions  of  the  body, 
simple  proteins  furnish  only  five.  The  remaining  ten  elements 
are  largely  constituents  of  the  ash  of  the  food  and  are  known  as 
ash  constituents,  inorganic  foodstuffs,  mineral  matter,  or  salts. 

Recent  investigations  have  developed  the  fact  that  food  of 
sufficient  energy  value  and  containing  ample  amounts  of  each 
of  the  chemical  elements  known  to  be  essential  to  the  body  is 
not  necessarily  adequate  to  meet  all  the  requirements  of  nutri- 
tion. Thus  it  appears  that  certain  substances  occurring  in 
natural  foods  but  not  yet  chemically  identified  are  also  to  be 
included  among  the  nutritive  requirements  of  the  body  and 


INTRODUCTION  Xlll 

therefore  among  the  factors  which  determine  the  nutritive 
values  of  foods.  At  present  these  unidentified  substances  are 
referred  to  as  "vitamines"  or  as  "fat  soluble  A"  and  "water 
soluble  B." 

The  essentials  of  a  chemically  adequate  food  supply  may 
therefore  be  summarized  as  follows :  (i)  sufficient  of  the  organic 
nutrients  in  digestible  forms  to  yield  the  needed  energy ;  (2)  pro- 
tein, sufficient  in  amount  and  appropriate  in  kind ;  (3)  adequate 
amounts  and  proper  proportions  of  the  various  ash  constituents 
or  inorganic  foodstuffs;  (4)  sufficient  of  each  of  the  two  un- 
identified "vitamine"  factors,  the  "fat  soluble  A"  and  the 
"water  soluble  B." 

In  attempting  to  give  in  the  following  pages  a  general  view 
of  the  chemistry  of  food  and  nutrition  it  has  seemed  best  to 
discuss  first  the  chemical  nature  and  nutritive  functions  of  the 
substances  which  serve  as  sources  of  energy  in  nutrition,  then 
the  nutritive  requirements  in  terms  of  energy,  protein,  the  more 
prominent  "inorganic"  elements,  and  the  "vitamines,"  and 
finally  the  bearing  of  these  various  factors  of  food  value  upon 
problems  connected  with  the  economic  use  of  food. 


CHEMISTRY  OF  FOOD 
AND  NUTRITION 


CHAPTER  I 
CARBOHYDRATES 

Of  the  constituents  of  the  ordinary  mixed  food  of  man  the 
carbohydrates  are  usually  the  most  abundant  and  the  most 
economical  sources  of  energy.  They  are  also  considered  to  be 
the  first  of  the  three  great  groups  of  foodstuffs  to  be  formed  by 
synthesis  from  simple  inorganic  substances  in  plants ;  "in  the 
long  run,  all  the  energy  of  living  matter  comes  from,;them." 
The  synthesis  of  carbohydrates  in  nature  is  therefore  a  logical 
starting  point  for  the  study  of  the  organic  foodstuffs. 

In  the  chlorophyll  cells  of  the  leaves  of  green  plants  the 
energy  of  the  sun's  rays  brings  about  reaction  between  carbon 
dioxide  and  water  which  results  in  the  Uberation  of  oxygen  and 
the  formation  of  organic  compounds.  There  is  still  doubt  as 
to  the  exact  mechanism  of  the  process  and  no  certainty  that  it 
is  the  same  in  all  cases.  It  has,  however,  been  quite  generally 
found  that  the  volume  of  oxygen  liberated  is  equal  to  that  of 
carbon  dioxide  consumed.  The  simplest  possible  representa- 
tion of  the  reaction  would  be 

CO2  +  H2O  -^  CH2O  +  O2 

according  to  which  the  first  product  of  the  synthesis  would  be 
formaldehyde.  There  is  considerable  (though  not  conclusive) 
evidence  that  formaldehyde  is  thus  formed  and  that  it  is  rapidly 
built  up  into  less  reactive  compounds.     Whatever  the  steps  in 


2  /        ;CilEMISTRY   O?  FOOD  AND   NUTRITION 

the  process*  there  is  normally  an  early  production  of  carbo- 
hydrate. Usually  the  first  product  which  can  be  demonstrated 
as  accumulating  in  the  plant  as  the  result  of  the  photosynthesis 
is  a  sugar  (glucose  or  sucrose)  or  starch.  Assuming  glucose  as 
a  typical  product  and  neglecting  the  intermediate  stages,  the 
photosynthesis  of  carbohydrate  may  be  represented  thus : 
6  CO2  +  6  H2O  ->  CeHiaOe  +  6  O2 

Glucose  is  the  most  familiar  representative  of  a  group  of  simple 
sugars  (monosaccharides  or  monosaccharoses)  which  are  in 
composition  direct  polymers  of  formaldehyde  (CH2O)  and  which 
are  classified,  according  to  the  number  of  carbon  atoms  in  the 
monosaccharide  molecule,  as  trioses,  pentoses,  hexoses,  etc. 

Classification 

Definitions  of  the  term  "  simple  sugar  "  vary  somewhat,  de- 
pending chiefly  upon  the  views  of  different  authors  as  to  how 
simple  a  compound  may  properly  be  called  a  sugar. 

According  to  Browne,  a  simple  sugar  or  monosaccharide  may 
be  defined  as  an  aldehyde  alcohol  or  ketone  alcohol  of  the  ali- 
phatic series,  the  molecule  of  which  contains  one  carbonyl  and 
one  or  more  alcohol  groups,  one  of  the  latter  being  always 
adjacent  to  the  carbonyl  group.  All  simple  sugars  contain," 
therefore, 

HC-OH 

I 

c=o 

I 


*  For  concise  discussion  of  the  synthesis  of  carbohydrates  in  plants  the  reader 
may  be  referred  to  Armstrong's  The  Simple  Carbohydrates  and  the  Glucosides,  pages 
92-g6;  Browne's  Handbook  of  Sugar  Analysis,  pages  532-534;  and  Mathews* 
Physiological  Chemistry,  pages  44-49.  A  somewhat  fuller  account  will  be  found  in 
Jost's  Pflanzenphysiologie  and  Euler's  Pflanzenchemie,  and  a  very  detailed  treatment 
of  the  subject  in  Czapek's  Biochemie  der  PJlanzen.  For  discussion  from  a  more 
physiological  standpoint,  see  Pfeffer's  Plant  Physiology  and  summary  of  recent 
work  by  Jorgenson  and  Stiles  in  The  New  Phytologist. 


CARBOHYDRATES  3 

as  a  characteristic  group  upon  the  presence  of  which  the  chief 
chemical  properties  of  the  sugars  depend. 

The  simplest  possible  sugar  according  to  this  definition  is 
glycolaldehyde,  CH2OH — CHO,  which  (in  analogy  with  the 
nomenclature  of  the  famiUar  sugars)  may  also  be  called  gly co- 
lose.  The  structural  formulae  of  glucose  and  fructose,  the  most 
familiar  representatives  of  the  aldehyde-alcohol  (aldose)  and 
ketone-alcohol  (ketose)  sugars,  respectively,  are  as  follows: 

Glucose  Fructose 

CH2OH  CH2OH 

I  I 

HOCH         HOCH 

I  I 

HOCH         HOCH 

I  I 

HCOH         HCOH 

I  I 

HOCH  C=0 

I  I 

HC=-0  CH2OH 


Since  glucose  gives  aldehyde  reactions  but  not  so  readily 
as  the  above  structural  formula  would  lead  one  to  expect,  it  is 
belJeved  that  in  ordinary  solutions  of  glucose  the  substance 
exists  partly  in  the  condition  indicated  by  the  aldehyde  formula 
and  partly  in  a  tautomeric  form  represented  by  the  lactone  or 
"  oxygen  bridge  "  formula. 

Following  are  the  aldehyde  and  lactone  formulae  written 
without  reference  to  the  spatial  relationships  of  the  hydrogen 
and  hydroxyl  groups : 

Aldehyde  form : 

CHoOH— CHOH— CHOH— CHOH— CHOH— CHO 

Lactone  form  :  O i 

CH2OH— CHOH— CH— CHOH— CHOH— CHOH 


4  CHEMISTRY  OF  FOOD  AND  NUTRITION 

The  name  monosaccharide  {"  single  sugar  ")  implies  that  the 
monosaccharide  molecule  contains  only  one  sugar  radicle  —  that 
it  cannot  be  split  by  hydrolysis  into  sugars  of  lower  molecular 
weight.  A  substance  like  cane  sugar  which  on  hydrolysis  spHts  to 
two  molecules  of  simple  sugar  is  called  a  disaccharide  or  disaccha- 
rose  ("  double  sugar  ")•  Trisaccharides  and  tetrasaccharides 
are  also  known.  Substances  which  like  starch  are  of  high  mo- 
lecular weight  and  on  complete  hydrolysis  yield  many  molecules 
of  simple  sugar  are  called  polysaccharides  *  or  polysaccharoses. 
The  term  "  carbohydrates  "  covers  all  the  simple  sugars  and 
all  substances  which  can  be  converted  into  simple  sugars  by  hy- 
drolysis. The  term  "  glucosides  "  is  appHed  to  substances  which 
consist  of  combinations  of  carbohydrate  radicles  with  radicles 
of  other  kinds  and  which  therefore  yield  on  hydrolysis  both  a 
simple  sugar  and  one  or  more  products  of  other  than  carbohy- 
drate nature. 

CLASSIFICATION  OF  CARBOHYDRATES  f 
MONOSACCHARIDES  (Monosaccharoses) 
Dioses  (C2H4O2)  —  Glycolose. 
Trioses  (C3H6O3). 
Aldoses  —  Glycerose. 
Ketose  —  Dioxyacetone. 

Tetroses  (C4H8O4). 

Aldoses  —  Erythroge,^-Tl 
Ketosc-j^^  Eryihrulose.^ 

Pentoses  (CsHioOs). 

/'   Aldoses  —  Arabinose,2  Xylose,^  Ribose,^  Lyxose.' 
/      Ketoses  —  Araboketose^,  Xyloketose  (ketoxylose)  .^ 
[Methyl  pentoses  (CeHiWOe)  —  Rhamnose,^  Fucose  ^j. 

*  Some  writers  use  the  term  polysaccharides  to  include  all  carbohydrates  other 
than  monosaccharides.  Mathews  applies  it  to  all  carbohydrates  more  complex  than 
the  disaccharides. 

t  Names  of  a  few  of  the  most  important  carbohydrates  are  printed  in  small 
capitals.  Separate  mention  of  the  d,  I,  and  dl  forms  of  the  various  sugars  is  omitted, 
since  in  the  study  of  food  and  nutrition  we  are  practically  concerned  only  with  that 
one  of  the  three  forms  which  is  found  in  or  derived  from  natural  products. 


CARBOHYDRATES  5 

Hexoses  (C6H12O6). 

Aldoses  —  Glucose,!  Mannose,^  Galactose,^  Gulose,^  Idose,'  Talose,^ 

Allose,3  Altrose.3 
Ketoses  —  Fructose/  Sorbose,^  Tagatose.^ 

Heptoses  (CtHhOv). 

Aldose  —  Mannoheptose.i 
Ketose —  Sedoheptose.^ 

Note.  —  No  attempt  is  here  made  to  summarize  the  occurrence  of  any  but  the 
tetroses,  pentoses,  hexoses  and  heptoses.  Glycolose  and  the  trioses  if  formed  in 
nature  are  probably  too  reactive  to  acciunulate  sufficiently  for  identification. 

DISACCHARIDES  (Disaccharoses). 
Dihexoses  (Hexobioses)  —  (C12H22O11). 
Anhydride  of  glucose  +  fructose  —  Sucrose. 
Anhydrides  of  glucose  +  galactose  —  Lactose,  Melibiose. 
Anhydrides  of  glucose -{- glucose  —  Maltose,   Isomaltose,    Trehalose, 
Turanose. 

TRIS ACCHARIDES  (Trisaccharoses) . 

Trihexoses  (C18H32O16). 

Anhydride  of  glucose  +  galactose  -\-  fructose —  Raffinose. 
Anhydride  of  glucose  +  glucose  +  glucose  —  Melezitose. 
Anhydride  of  fructose  -{-fructose  -{-fructose —  Secalose. 

TETRA SACCHARIDES  (Tetrasaccharoses) . 

Tetrahexoses  (C24H42O21). 

Anhydrides  of  2  galactose  +  glucose  -{-fructose  —  Stachyose,  Lupeose. 

POLYSACCHARIDES  (Polysaccharoses) . 
Pentosans  (chief  constituents  of  gums  and  mucilages). 

Anhydrides  of  xylose  —  Xylans. 

Anhydrides  of  arahinose  —  Arabans. 
Hexosans. 

Anhydrides   of  glucose — Starch,   Cellulose,   Glycogen,  Dextrin 
(and  other  "  dextraias  ") .  ^ 

Anhydrides  of  mannose  —  Mannans. 

Anhydrides  of  galactose —  Galactans  (pectins). 

Anhydrides  of  fructose —  Inulin  (and  other  "levulans"). 

!  Occurs  free  in  nature. 

2  Not  yet  found  free  in  nature  (or  only  in  small  amounts)  but  obtained  by  hy- 
drolysis or  fermentation  of  natural  product. 

^  Known  only  (with  certainty)  as  a  laboratory  product. 


6  CHEMISTRY  OF  FOOD  AND  NUTRITION 

TROPERTIES   OF  THE   CHIEF  CARBOHYDRATES  OF  FOOD 
Monosaccharides 

The  monosaccharides  are  all  soluble,  crystaUizable,  diffusible 
substances,  unaffected  by  digestive  enzymes,  and  if  not  attacked 
by  bacteria  in  the  digestivp  tract,  they  are  absorbed  and  enter  the 
blood  current  unchanged.  All  of  the  three  hexoses  described 
below  are  susceptible  to  alcoholic  fermentation,  aAd  are  utilized 
for  the  production  of  glycogen  in  the  animal  body  and  the 
maintenance  of  the  normal  glucose  content  of  the  blood.  A 
few  of  the  leading  facts  regarding  the  occurrence  in  food  and 
the  nutritive  relations  of  individual  monosaccharides  are  given 
below. 

Glucose  W.glucose,  dextrose,  grape  sugar,  starch  sugar, 
diabetic  sugar)  is  widely  distributed  in  nature,  occurxing  in 
the  blood  of  all  animals  in  small  quantity  (usually  about  o.i  per 
cent)  and  more  abundantly  in  fruits  and  plant  juices,  where  it 
is  usually  associated  with  fructose  and  sucrose.  It  is  especially 
abundant  in  grapes,  of  which  it  often  constitutes  20  per  cent 
or  more  of  the  weight  of  the  fresh  fruit  and  considerably  more 
than  half  of  the  soHd  matter.  Sweet  corn,  onions,  and  unripe 
potatoes  are  among  the  common  vegetables  containing  con- 
siderable amounts  of  glucose. 

Glucose  is  also  obtained  from  many  other  carbohydrates  by 
hydrolysis  either  by  acids  or  by  enzymes,  and  thus  becomes  the 
principal  form  in  which  the  carbohydrate  of  the  food  enters  into 
the  animal  economy.  In  the  healthy  animal  body  the  glucose 
of  the  blood  is  constantly  being  burned  and  replaced.  In  dia- 
betes the  body  loses  to  a  greater  or  less  degree  the  power  to 
burn  glucose,  which  then  accumulates  in  excessive  amount  in 
the  blood,  from  which  it  escapes  through  the  kidneys.  A  tem- 
porary and  usually  unimportant  loss  of  glucose  in  the  urine 
may  occur  as  the  result  of  feeding  large  quantities  at  a  time. 
This  condition  is  known  as  aUmentary  glycosuria.    Ordinarily 


CARBOHYDRATES  7 

any  surplus  of  glucose  absorbed  from  the  digestive  tract  is  con- 
verted into  glycogen  which,  as  described  beyond,  is  readily 
reconvertible  into  glucose.  Thus,  while  other  carbohydrates 
occur  in  food  in  greater  quantity,  glucose  occupies  a  very  prom- 
inent place,  partly  because  it  is  more  widely  distributed  than 
any  other  carbohydrate,  being  a  normal  constituent  of  both 
plants  and  animals,  and  partly  because  it  is  the  form  in  which 
most  of  the  carbohydrate  material  of  the  food  comes  ultimately 
into  the  service  of  the  body  tissues  (Chapter  V).  It  is  esti- 
mated that  over  half  the  energy  manifested  in  the  human  body 
is  derived  from  the  oxidation  of  glucose. 

It  is  not  to  be  inferred  from  the  foregoing  statement  that 
the  body  obtains  the  energy  of  the  glucose  by  oxidizing  it  di- 
rectly as  such.  The  aldehydic  properties  of  glucose  make  it 
susceptible  to  direct  oxidation ;  but,  as  the  elaborate  researches 
of  Nef  have  shown,  the  glucose  molecule  in  alkaline  solution 
breaks  up  to  form  simpler  substances  of  2,  3,  and  4  carbon 
atoms  which  are  more  readily  oxidizable  than  glucose  itself. 
There  is  strong  evidence  (Chapter  V)  that  in  the  body  tissues 
glucose  is  broken  into  3-carbon  molecules,  which  latter  readily 
undergo  oxidation. 

Fructose  (^i. fructose,  fruit  sugar,  levulose)  occurs  with  more 
or  less  glucose  in  plant  juices,  in  fruits,  and  especially  in  honey, 
of  which  it  constitutes  about  one  half  the  soHd  matter.  It 
results  in  equal  quantity  with  glucose  from  the  hydrolysis  of 
cane  sugar  and  in  smaller  proportion  from  some  other  less 
common  sugars.  Fructose  may  occur  in  normal  blood,  but 
probably  only  in  insignificant  amounts.  It  serves,  Hke  glu- 
cose, for  the  production  of  glycogen;  and  the  fructose  which 
enters  the  body  either  through  being  eaten  as  such  or  as  the 
result  of  the  digestion  of  cane  sugar  is  mainly  changed  to  gly- 
cogen on  reaching  the  liver,  so  that  it  does  not  enter  largely 
into  the  blood  of  the  general  circulation.  Glucose  and  fructose 
are  partially  convertible,  either  one  into  the  other,  under  the 


8  CHEMISTRY  OF  FOOD  AND   NUTRITION 

influence  of  very  dilute  alkalies.  It  is  not  surprising,  there- 
fore, that  fructose  should  be  converted  in  the  liver  into  glycogen, 
which  on  hydrolysis  yields  glucose. 

Galactose  is  not  found  free  in  nature,  but  results  from  the 
hydrolysis  of  milk  sugar,  either  by  acids  or  by  digestive  enzymes, 
and  appears  to  have  the  same  power  as  glucose  and  fructose  to 
promote  the  formation  of  glycogen  in  the  animal  body.  Anhy- 
drides of  galactose,  known  as  galactans,  occur  quite  widely 
distributed  in  plants ;  and  galactosides,  which  are  compounds 
containing  galactose  in  chemical  combination  with  radicles 
of  other  than  carbohydrate  nature,  are  found  in  the  animal 
body,  notably  as  constituents  of  the  brain  and  nerve  tissues. 

Disaccharides 

The  three  disaccharides  here  considered  are  di-hexoses  or 
hexo-bioses  of  the  formula  C12H22O11,  and  are  crystalHzable 
and  diffusible.  Sucrose  crystallizes  anhydrous;  maltose  and 
lactose,  each  with  one  molecule  of  water,  which  can  be  removed 
by  drying  at  temperatures  of  100°  and  130°  respectively. 
They  are  soluble  in  water;  less  soluble  in  alcohol.  Lactose 
is  much  less  soluble  than  sucrose  and  maltose.  These  disac- 
charides are  important  constituents  of  food  and  are  changed  to 
monosaccharides  during  the  process  of  digestion. 

Sucrose  (saccharose,  cane  sugar)  is  widely  distributed  in  the 
vegetable  kingdom,  being  found  in  considerable  quantity, 
generally  mixed  with  glucose  and  fructose,  in  the  fruits  and 
juices  of  many  plants.  The  commercially  important  sources 
of  sucrose  are  the  sugar  beet,  the  sugar  and  sorghum  canes,  the 
sugar  palm,  and  the  sugar  maple;  but  many  of  the  common 
fruits  and  vegetables  contain  notable  amounts.  For  example, 
sucrose  is  said  to  constitute  at  least  half  the  solid  matter  of 
pineapples  and  of  some  roots  such  as  carrots. 

On  hydrolysis  each  molecule  of  sucrose  3delds  one  molecule 


CARBOHYDRATES  9 

each  of  glucose  and  fructose.  These  sugars  all  rotate  the  plane 
of  vibration  of  polarized  light,  sucrose  and  glucose  to  the  right 
(+),  and  fructose  to  the  left  (— ).  The  terms  "dextrose" 
and  "  levulose,"  synonyms  for  glucose  and  fructose  respectively, 
arose  from  this  behavior  of  the  sugars  in  rotating  the  plane  of 
polarized  light  to  the  right  and  left.  Since  at  ordinary  tem- 
peratures the  fructose  rotates  more  strongly  to  the  left  than  the 
glucose  does  to  the  right,  the  result  of  the  hydrolysis  of  sucrose 
is  to  change  the  sign  of  rotation  from  +  to  — .  For  this  reason 
the  hydrolysis  of  cane  sugar  is  often  called  "  inversion,"  and 
the  resulting  mixture  of  equal  parts  glucose  and  fructose  is 
known  as  "  invert  sugar." 

Sucrose  is  very  easily  hydrolyzed  either  by  acid  or  by  the 
sucrase  ("  invertase  "  or  "  inverting  "  enzyme)  of  yeast  or  of 
intestinal  juice.  So  far  as  known  neither  the  saliva  nor  the 
gastric  juice  contains  any  enzyme  capable  of  hydrolyzing  cane 
sugar,  and  the  slight  amount  of  hydrolysis  which  takes  place 
in  the  stomach  is  believed  to  be  due  simply  to  the  presence  of 
hydrochloric  acid.  Under  normal  conditions  the  sucrose  of 
the  food  passes  mainly  into  the  intestine  unchanged  and  is 
there  spHt  by  the  sucrase  of  the  intestinal  juice,  and  the  result- 
ing glucose  and  fructose  are  absorbed  into  the  portal  blood. 

When  large  amounts  of  sucrose  are  fed,  some  absorption  takes 
place  in  the  stomach;  but  the  unchanged  sucrose  thus  ab- 
sorbed appears  to  be  largely,  if  not  wholly,  lost  through  the 
kidneys,  as  it  is  when  injected  directly  into  the  blood  current. 
Sugar  eaten  in  concentrated  form  or  in  considerable  quantities 
at  a  time  is  apt  to  cause  irritation  of  the  stomach  either  directly, 
or  as  the  result  of  undergoing  an  acid  fermentation,  or  in  both 
of  these  ways.  According  to  Herter  sucrose  and  glucose  are 
more  Hkely  to  ferment  in  the  stomach  than  is  lactose.  In  cases 
where  fermentation  does  not  occur  and  the  sucrose  itself  has  no 
irritating  effect,  it  may  be  especially  useful  as  a  rapidly  avail- 
able foodstuff.     However,  it  is  not  known  that  sucrose  has  any 


lO  CHEMISTRY  OF  FOOD  AND  NUTRITION 

advantage  over  maltose  and  lactose  in  this  respect,  and  the 
latter  are  less  apt  to  irritate  the  stomach  and  cause  indigestion. 

Lactose  (milk  sugar)  occurs  in  the  milk  of  all  mammals, 
constituting  usually  from  6  to  7  per  cent  of  the  fresh  secretion 
in  human  milk  and  4.5  to  5  per  cent  in  the  milk  of  cows  and 
goats.  At  the  time  of  parturition,  or  if  the  milk  is  not  with- 
drawn from  the  udder,  some  lactose  may  occur  in  the  urine.  If 
in  such  a  case  the  mammary  glands  are  removed,  the  percentage 
of  glucose  in  the  blood  increases,  and  glucose  (but  no  lactose) 
may  appear  in  the  urine  (Abderhalden).  These  observations 
indicate  that  lactose  is  formed  in  the  mammary  gland  and  prob- 
ably from  the  glucose  brought  by  the  blood. 

Lactose  is  less  sweet  and  much  less  soluble  than  sucrose,  dis- 
solving only  to  the  extent  of  about  i  part  in  6  parts  of  water. 

When  hydrolyzed  either  by  heating  with  acids  or  by  an 
enzyme,  such  as  emulsin  or  the  lactase  of  the  intestinal  juice, 
each  molecule  of  lactose  yields  one  molecule  of  glucose  and 
one  of  galactose.  In  normal  digestion,  probably  none  of  the 
lactose  eaten  is  absorbed  as  such,  for  lactose  injected  into  the 
blood  is  eliminated  quickly  and  almost  completely  through  the 
kidneys,  whereas  large  amounts  of  lactose  can  be  taken  by  the 
mouth  without  any  such  loss.  As  already  noted,  Herter  found 
lactose  to  be  less  subject  to  fermentation  in  the  stomach  than  is 
sucrose.  Also,  because  of  the  much  lower  solubility,  there  is 
less  danger  of  direct  irritation  of  the  stomach  membrane  by 
lactose  than  by  sucrose.  Recently  Mathews  has  suggested  that 
the  occurrence  in  milk  of  lactose,  a  sugar  having  the  galactose 
radicle,  may  be  6i  special  significance  as  a  source  of  material 
for  the  synthesis  of  the  galactosides  of  the  brain  and  nerve 
tissues  of  the  rapidly  growing  young  mammal. 

Maltose  (malt  sugar)  is  formed  from  starch  by  the  action 
of  diastatic  enzymes  (amylases)  and  is  therefore  an  important 
constituent  of  germinating  cereals,  malt,  and  malt  products. 
It  is  also  formed  as  an  intermediate  product  when  starch  is 


CARBOHYDRATES  II 

hydrolyzed  by  boiling  with  dilute  mineral  acids,  as  in  the 
manufacture  of  commercial  glucose. 

In  animal  digestion  maltose  is  formed  by  the  action  of  the 
ptyalin  of  the  saliva  or  the  amylopsin  of  the  pancreatic  juice 
upon  starch  or  dextrin.  The  maltose-spHtting  enzyme  of  the 
intestinal  juice  readily  hydrolyzes  maltose  to  glucose.  Maltose 
is  also  readily  and  completely  hydrolyzed  by  boiling  with  dilute 
minej-al  acids.  In  either  case  each  molecule  of  maltose  yields 
two  molecules  of  glucose. 

While  it  is  probable  that  little  if  any  maltose  is  absorbed  as 
such  from  the  digestive  tract  under  ordinary  conditions,  it  is 
possible  that  such  absorption  may  occur  and  that  maltose  as 
such  may  play  a  part  in  the  normal  carbohydrate  metabolism ; 
for  when  injected  into  the  blood  it  appears  to  be  utilized  to 
better  advantage  than  either  sucrose  or  lactose,  and  it  may  be 
obtained  from  glycogen  by  the  action  of  diastatic  enzymes  in 
much  the  same  way  as  from  starch  and  dextrin. 

Polysaccharides 

The  polysaccharides  are  all  colloids  insoluble  in  alcohol. 
Some  "  dissolve  "  in  water  in  the  sense  that  they  form  colloidal 
dispersions  which  will  pass  through  filter  paper;  some  swell 
and  become  gelatinous ;  some  are  unchanged.  The  members  of 
greatest  importance  in  nutrition  are  starch  and  glycogen,  the 
typical  reserve  carbohydrates  of  plants  and  animals  respectively. 

Pentosans,  (C5H804)a;,  occur  in  the  greatest  variety  of  plants 
and  in  various  parts  of  the  plant  organism.  As  a  rule,  how- 
ever, they  are  abundant  only  in  the  fibrous  tissues  and  gummy 
exudations  and  not  in  the  starchy  and  succulent  parts  which 
are  more  commonly  used  for  human  food.  Moreover  experi- 
ments have  not  yet  succeeded  in  demonstrating  in  man  or 
other  mammals  any  enzyme  capable  of  digesting  the  pentosans 
(Swartz).     It  is  therefore  believed  that,  notwithstanding  their 


12  CHEMISTRY  OF  FOOD  AND  NUTRITION 

wide  distribution  in  plants,  the  pentosans  can  play  only  a  very 
small,  if  appreciable,  part  in  the  nutrition  of  man. 

Starch,  (CeHioOs)!,  is  the  form  in  which  most  plants  store 
the  greatest  part  of  their  carbohydrates,  and  is  of  great  im- 
portance as  a  constituent  of  many  food  materials  and  as  the 
source  of  dextrin,  maltose,  commercial  glucose,  and  many  fer- 
mentation products.  Starch  is  found  stored  in  the  seeds,  roots, 
tubers,  bulbs,  and  sometimes  in  the  stems  and  leaves  of  plants. 
It  constitutes  one  half  to  three  fourths  of  the  solid  matter 
of  the  ordinary  cereal  grains  and  at  least  three  fourths  of  the 
sohds  of  mature  potatoes. 

Unripe  apples  and  bananas  contain  much  starch  which  is 
to  a  large  extent  changed  into  sugars  as  these  fruits  ripen, 
while,  on  the  other  hand,  young  tender  corn  (maize)  kernels 
and  peas  contain  sugar  which  is  transformed  into  starch  as  these 
seeds  mature. 

Unchanged  starch  occurs  in  distinct  granules,  and  those 
formed  in  different  plants  vary  in  size  and  structure,*  so  that 
in  most  cases  the  source  of  a  starch  which  has  not  been  alt^ed 
by  heat,  reagents,  or  ferments  can  be  determined  by  microscopi- 
cal examination.  Starch  granules  are  scarcely  affected  by  cold 
water ;  on  warming  they  absorb  water  and  swell.  Finally  the 
starch  passes  into  a  condition  of  colloidal  dispersion  ^r  semi- 
solution,  "  starch  paste."  Starch  "which  Tias  been  heated  in 
water  (either  admixed  or  naturally  present  with  the  starch  as 
in  a  potato)  until  the  granules  are  ruptured  and  the  material 
more  or  less  dispersed  is  very  much  more  rapidly  hydrolyzed  by 
digestive  ferments  than  is  raw  starch. 

To  colloids  such  as  starch,  the  usual  methods  of  determining 
molecular  weight  are  not  applicable.  It  is  certain,  however, 
from  the  chemical  complexity  of  some  of  the  dextrins  which 

.  *  A  very  detailed  study  of  the  starch  granules  of  different  species  of  plants  has 
been  made  by  Reichert  and  published  by  the  Carnegie  Institution  of  Washington. 
(See  references  at  end  of  chapter.) 


CARBOHYDRATES  13 

result  from  hydrolysis  of  starch,  that  the  molecular  weight  of 
starch  must  be  very  high  and  its  chemical  constitution  very 
complex.  Probably  the  value  of  x  in  the  formula  (CeHioOo)! 
is  very  large,  perhaps  in  the  neighborhood  of  200,  corresponding 
to  a  molecular  weight  of  about  32,000.  For  a  full  discussion  of 
the  more  important  facts  bearing  on  the  chemical  constitution 
'of  starch,  see  the  paper  by  Thomas  cited  in  the  list  of  refer- 
ences at  the  end  of  the  chapter. 

Starch  either  in  the  solid  or  in  the  "  soluble  "  (dispersed) 
form  is  colored  intensely  blue  when  treated  with  iodine.  This 
well-known  reaction  is  delicate  and  distinctive,  but  is  now  be- 
lieved to  be  due  to  colloidal  adsorption  rather  than  to  the  for- 
mation of  a  definite  chemical  compound. 

The  term  "  starch,"  as  we  ordinarily  use  it,  probably  covers  at 
least  two  substances.  The  more  abundant  of  these,  a-amylose 
(also  called  "  amylopectin  "),  forms  on  heating  in  water  a 
viscous  opalescent  paste,  gives  a  somewhat  purplish  blue  color 
with  iodine,  is  evidently  of  great  molecular  complexity,  and 
has.  recently  been  found  to  contain  a  small  amount  of  phos- 
phorus *  as  an  essential  constituent.  The  less  abundant  com- 
ponent of  starch,  /8-amylose  (also  called  "  amylose  "),  forms 
when  heated  in  water  a  clear,  limpid  solution  which  gives  a 
pure  blue  color  with  iodine.  The  starch-digesting  enzymes 
hydrolyze  both  a-amylose  and  /8-amylose,  but  not  always  with 
equal  facihty.f 

Starch  on  hydrolysis  by  means  of  acid  gives  first  mixtures  of 
dextrin  and  maltose,  and  finally  glucose  only  as  an  end-product. 
The  most  satisfactory  hydrolysis  of  starch  to  glucose  is  ac- 
complished by  boihng  or  heating  in  a  boiling  water  bath  with 
hydrochloric  acid  of  a  concentration  of  about  2.5  per  cent. 
When  brought  in  contact  with  saUva,  starch  is  hydrolyzed  by 

*  In  the  case  of  potato  starch  about  0.06  per  cent.  See  papers  by  Northrup 
and  Nelson  and  by  Thomas  referred  to  at  the  end  of  the  chapter. 

t  See  paper  by  Sherman  and  Baker  referred  to  at  the  end  of  the  chapter. 


14  CHEMISTRY  OF  FOOD  AND  NUTRITION 

the  ptyalin,  with  the  formation  of  dextrin  and  maltose.  A 
similar  hydrolysis  is  affected  by  "  amylopsin,"  the  starch- 
splitting  enzyme  of  the  pancreatic  juice,  preferably  known 
as  pancreatic  amylase  (see  terminology  of  enzymes,  Chapter 
IV). 

*'  Soluble  starch,"  largely  used  for  laboratory  experiments,  is 
usually  prepared  by  soaking  raw  starch  in  cold  hydrochloric 
acid  (about  7  per  cent  HCl)  for  several  days,  and  then  washing 
with  cold  water. 

Dextrins,  (CeHioOs)^  or  (C6Hio05)x-H20,  are  formed  from 
starch  by  the  action  of  enzymes,  acids,  or  heat.  Small  amounts 
of  dextrin  are  found  in  normal,  and  larger  amounts  in  germi- 
nating, cereals.  Malt  diastase,  acting  for  some  time  upon  starch 
in  fairly  concentrated  solution,  yields  usually  about  one  part 
of  dextrin  to  four  of  maltose.  During  acid  hydrolysis,  dextrin 
is  formed  as  an  intermediate  product  between  soluble  starch 
and  maltose.  Commercial  dextrin,  the  principal  constituent 
of  "  British  gum,"  is  obtained  by  heating  starch,  either  alone 
or  with  a  small  amount  of  dilute  acid. 

The  dextrins  are  much  more  soluble  than  the  starches ;  and 
dextrin  molecules  while  doubtless  very  large  and  complex  are 
probably  not  over  one  fifth  the  size  of  starch  molecules. 

The  digestion  of  dextrin  has  already  been  mentioned  in 
connection  with  that  of  starch,  both  saliva  and  pancreatic  juice  * 
forming  dextrin  during  the  digestion  of  starch  and  acting  upon 
it  with  the  production  of  maltose.  Complete  hydrolysis  of 
dextrin,  as  by  boiHng  with  acid,  yields  glucose  as  the  sole 
product. 

Glycogen,  (CeHioOs)^,  plays  much  the  same  role  in  animals 
which  starch  plays  in  plants,  and  is  sometimes  called  "  animal 
starch."  Glycogen  also  takes  the  place  of  starch  as  reserve 
carbohydrate  in  fungi  and  other  forms  of  plant  life  not  pro- 
vided with  the  chlorophyll  apparatus.  It  is  a  white,  amor- 
phous powder,  odorless  and  tasteless,  which  swells  up  and  ap- 


CARBOHYDRATES  15 

parently  dissolves  in  cold  water  to  an  opalescent  colloidal  dis- 
persion which  is  not  cleared  by  repeated  filtration,  but  loses  its 
opalescence  on  addition  of  a  very  small  amount  of  potassium 
hydroxide  or  acetic  acid.  Water  solutions  (dispersions)  of 
glycogen  are  readily  precipitated  by  alcohol.  When  treated 
with  iodine  they  react  yellow-brown,  red-brown,  or  deep  red. 
Hydrolysis  of  glycogen  yields  glucose  only,  as  end-product. 

Glycogen  occurs  in  the  lower  as  well  as  the  higher  animals, 
and  in  all  parts  of  the  body,  but  is  especially  abundant  in  the 
liver.  The  amount  of  glycogen  in  the  liver  depends  to  a  great 
extent  upon  the  condition  of  nutrition  of  the  animal.  In  the 
average  of  seven  experiments  by  Schondorff  in  which  dogs  were 
fed  for  the  production  of  as  much  glycogen  as  possible,  38  per 
cent  of  that  found  was  in  the  liver,  44  per  cent  in  the  muscles, 
9  per  cent  in  the  bones,  and  the  remaining  9  per  cent  in  the 
other  tissues  of  the  body.  But  the  distribution  of  glycogen  in 
the  body  as  shown  by  these  experiments  was  quite  variable, 
even  among  animals  of  the  same  species  which  had  been  fed 
in  the  same  way.  It  is  well  known,  too,  that  some  species 
store  glycogen  in  their  muscles  to  a  greater  extent  than  others, 
attempts  even  having  been  made  to  distinguish  analytically 
between  horseflesh  and  beef  by  the  difference  in  their  glycogen 
content.  The  storage  of  glycogen  in  the  body  is  promoted  by 
rest  as  well  as  by  liberal  feeding,  and  stored  glycogen  is  used 
up  rapidly  during  active  muscular  work. 

Cellulose,  (CeHioOs)^;,  the  chief  constituent  of  wood  and  of 
the  walls  of  plant  cells  generally,  is  an  anhydride  of  glucose 
and  can  be  made  to  yield  the  latter  when  hydrolyzed  by  suit- 
able treatment  with  strong  acid.  Typical  cellulose  of  mature 
fiber  (such  as  cotton,  Hnen,  or  wood  fiber)  is,  however,  quite 
resistant  to  the  action  of  dilute  acids  or  of  ordinary  enzymes  and 
passes  through  the  digestive  tract  for  the  most  part  unchanged. 
The  toughness  of  the  cellulose  differs  with  the  stage  of  growth 
or  maturity,  and  some  of  the  less  resistant  forms  of  cellulose, 


l6  CHEMISTRY  OF  FOOD  AND   NUTRITION 

such  as  that  of  tender  white  cabbage,  may  disappear  from  the 
digestive  tract  in  appreciable  amounts.  Experiments  to  de- 
termine whether  the  cellulose  thus  disappearing  is  digested  to 
sugar  and  absorbed  or  merely  decomposed  by  bacteria  in  the 
digestive  tract  have  not  given  conclusive  results.  According 
to  Swartz :  "  In  any  event,  the  quantities  of  cellulose  which  the 
alimentary  tract  of  man  is  capable  of  absorbing  are,  apparently, 
too  small  for  it  to  play  a  r61e  of  any  importance  in  the  diet 
of  a  normal  individual."  The  cellulose  in  the.  food  may,  how- 
ever, serve  a  very  useful  purpose  in  giving  bulk  to  the  food 
residues  and  thus  facilitating  their  passage  along  the  digestive 
tract. 

Hemicelluloses  is  a  term  somewhat  loosely  applied  to  poly- 
saccharides, usually  occurring  as  constituents  of  cell  walls  in 
plants,  which  are  not  digested  by  the  starch-splitting  enzymes 
but  are  usually  much  more  readily  hydrolyzed  by  acid  than  is 
cellulose.  In  many  plant  tissues  the  hemicellulose  consists 
chiefly  of  pentosans ;  in  other  cases  it  is  largely  mannan  or  ga- 
lactan. 

M^nnans,  (CeHioOs)^,  anhydrides  of  mannose,  are  widely 
distributed  in  the  vegetable  kingdom  and,  as  Swartz  points  out, 
show  great  differences  in  solubility,  ranging  from  the  readily 
soluble  mucilaginous  forms  found  in  certain  legumes  to  the 
horny  matter  of  such  seeds  as  the  date,  a  form  of  mannan  which 
was  long  confused  with  true  cellulose.  The  experiments  of 
Swartz  upon  the  mannan  of  salep  showed  it  to  disappear  com- 
pletely in  its  passage  through  the  human  digestive  tract,  al- 
though tests  with  individual  digestive  enzymes  gave  negative 
results.  In  what  way  and  to  what  extent  the  mannan  thus  dis- 
appearing from  the  digestive  tract  becomes  available  in  nu- 
trition is  still  a  subject  of  investigation. 

Galactans,  (C6Hio05)a;,  anhydrides  of  galactose,  are  widely 
distributed  in  plants.  They  occur  in  the  seeds  of  legumes  and 
to  a  slight  extent  in  the  cereals  also,  in  by-products  of  beet 


CARBOHYDRATES  1 7 

sugar  manufacture  and  abundantly  in  several  of  the  algae  and 
lichens,  including  Chinese  moss,  agar-agar,  and  Irish  moss. 
The  pectins  are  said  to  consist  largely  of  galactans,  apparently 
either  in  combination  or  admixture  with  pentosans  and  perhaps 
other  complexes  as  well.  The  galactans  differ  in  their  solu- 
biHties  and  apparent  digestibility  when  eaten  by  man  or  other 
animals,  but  on  the  whole  do  not  appear  to  be  of  much  nutri- 
tive value.  Those  of  agar-agar  and  Irish  moss,  which  are  most 
used  as  food,  are  not  digested. 

Levulans  is  the  terin  under  which  a  number  of  polysaccharides 
of  the  composition  (CeHioOs)^,  and  )delding  fructose  (levulose) 
on  hydrolysis  have  been  described.  The  most  important  of 
these,  at  least  so  far  as  is  at  present  known,  is  inulin,  a  white, 
powdery  substance  occurring  in  the  tubers  of  the  Jerusalem 
artichoke  and  to^a  less  extent  in  the  bulbs  of  onions  and  garlic 
as  well  as  in  various  parts  of  plants  not  commonly  used  for 
food.  By  the  action  of  acids  inulin  is  very  readily  hydrolyzed 
to  levulose,  but  the  digestive  juices  do  not  seem  to  contain 
enzymes  capable  of  hydrolyzing  inuHn  and  it  appears  to  be  of 
practically  no  importance  as  human  food. 

REFERENCES 

Abderhalden.    Physiologische  Chemie  (3.  Aufl.). 

Abderhalden.     Biochemisches  Handlexicon. 

Abderhalden.    Handbuch  der  Biochemischen  Arbeitsmethoden. 

Armstrong.    The  Simple  Carbohydrates  and  the  Glucosides. 

Armstrong.    Article  on  Carbohydrates  in  Thorpe's  Dictionary  of  Applied 

Chemistry  (Revised  Edition). 
Browne.    Handbook  of  Sugar  Analysis. 
Cohen.    Organic  Chemistry. 
Czapek.     Biochemie  der  Pflanzen. 
Lippmann.     Chemie  der  Zuckerarten. 
Mathews.    Physiological  Chemistry. 
Nef.     (Behavior  of  the  sugars  toward  alkalies  and  oxidizing  agents.) 

Leibig's  Annalen  der  Chemie,  Vol.  357,  page  214;   Vol.  376,  page  i; 

Vol.  403,  page  204. 
c 


l8  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Northrop  and  Nelson.    The  Phosphorus  Content  of  Starch.    Journal 

of  the  American  Chemical  Society,  Vol.  38,  page  472  (19 16). 
Reichert.     The  Differentiation  and  Specificity  of  the  Starches  in  Relation 

to  Genera  and  Species.     Carnegie  Institution  of  Washington,  PubHca- 

tion  No.  173. 
ScHRYVER    AND    Haynes.     Pectin    Substances    of    Plants.      Biochemical 

Journal,  Vol.  10,  page  539  (1916). 
Sherman  and  Baker.     Experiments  upon  Starch  as  Substrate  for  Enzyme 

Action.    Journal  of  the  American  Chemical  Society,  Vol.  38,  page  1885 

(1916). 
SwARTZ.     Nutrition  Investigations  on  the  Carbohydrates  of  Lichens,  Algae 

and  Related  Substances.     Transactions  of  the  Connecticid  Academy  of 

Sciences,  Vol.  16,  pages  247-382  (1909). 
Thomas.    The    Phosphorus    Content    of    Starch.     Biochemical    Bulletin, 

Vol.  3,  page  403  (1914)- 
Thomas.    The   Chemical   Constitution   of  Starch.     Biochemical  Bulletin, 

Vol.  4,  page  379  (1915)- 
Tollens.     Kurzes  Handbuch  der  Kohlenhydrate. 


CHAPTER  II 

FATS   AND   LIPOIDS 

Almost  as  widely  distributed  in  nature  as  the  carbohydrates, 
and  constituting  a  much  more  concentrat^ed  form  of  fuel  to 
supply  energy  in  nutrition,  are  the  fats.  Fats  are  glyceryl 
esters  of  fatty  ^cids^}and  since  glycerol  is  a  triatomic  alcohol 
and  the  fatty  acids  are  monatomic,  a  normal  glyceride  is  a 
triglyceride  and  on  hydrolysis  yields  three  molecules  of  fatty 
acid  and  one  molecule  of  glycerol.    Thus,  for  example : 

C3H5(Ci8H3502)3  +  3  H2O  "^  C3H5(OH)3  +  3  C18H36O2. 
stearin  Glycerol  Stearic  acid 

(glyceryl  tristearate) 

\JVTien  the  spHtting  of  the  fat  is  brought  about  by  means  of  an 
alkaH  instead  of  water,  the  corresponding  products  are  glycerol 
and  three  molecules  of  the  alkali  salt  of  the  fatty  acid.  Since 
alkali  salts  of  the  fatty  acids  are  commonly  known  as  soaps, 
this  reaction  is  usually  called  saponification  of  the  fat. 

The  fats  are  therefore  a  definite  group  of  chemical  compounds, 
and  the  term  applies  equally  to  the  solid  and  the  Hquid  members 
of  this  group.  As  a  matter  of  convenience,  however,  the 
Hquid  fats  are  often  called  "  fatty  oils."  The  fatty  oils  are 
also  sometimes  called  "  fixed  oils,"  since  a  spot  made  by  drop- 
ping a  fatty  oil  on  paper  cannot  be  removed  by  drying  (as  can 
a  volatile  oil),  nor  by  washing  with  water  (as  can  glycerin). 

Another  property  which  helps  to  characterize  the  fats  is 
that  glycerol,  or  the  glyceryl  radicle  of  a  fat,  when  heated  to  a 
high  temperature  (300°  C.  or  over),  decomposes  with  production 
of  acrolein,  an  aldehyde  of  characteristic  odor  and  very  irritating 
to  the  mucous  membranes.     Doubtless  also  fatty  acid  radicles 

19 


20  CHEMISTRY  OF  FOOD   AND  NUTRITION 

may  sometimes  contribute  to  the  production  of  irritating  fumes 
when  fat  is  overheated. 

(The  fats,  including  fatty  oils,  are  lighter  than  water,  their 
specific  gravities  ranging  between  0.90  and  0.97.  They  are 
poor  conductors  of  heat  and  therefore  tend  to  conserve  the 
heat  of  the  body,  while  they  show  on  oxidation  a  much  higher 
fuel  value  than  any  of  the  other  foodstuffs. 
'  All  of  the  fats  are  practically  insoluble  in  water,  and  all  ex- 
cept those  of  the  castor  oil  group  are  sparingly  soluble  in  cold 
alcohol,  but  dissolve  readily  in  petroleum  ether  and  mix  in  all 
proportions  with  light  petroleum  oils.  Light  petroleum  dis- 
tillate {"  petroleum  ether  ")  is  often  used  as  a  solvent  for  fat. 
AH  of  the  fats  are  readily  soluble  in  ether,  carbon  bisulphide, 
chloroform,  carbon  tetrachloride,  and  benzene.  Since  neither 
carbohydrates,  proteins,  nor  ash  constituents  are  soluble  in 
ether  (or  the  other  "  fat  solvents  "),  it  follows  that  the  fat  of  a 
food  may  be  readily  separated  from  the  other  chief  components 
by  drying  the  food  and  extracting  the  dry  material  with  pure 
ether.  After  the  fat  has  been  completely  dissolved  away  from 
the  other  foodstuffs,  it  can  be  recovered  from  the  solvent  by 
evaporating  the  latter  at  a  relatively  low  temperature.  This 
is  the  method  commonly  used  to  estimate  the  percentages  of 
fat  in  foods  and  to  obtain  small  portions  of  fat  for  examination. 
It  must  be  noted,  however,  that  the  fat  thus  obtained  is  not 
always  pure  in  the  sense  of  consisting  entirely  of  substances 
meeting  the  definition  of  fat  as  given  above.  Obviously,  such 
an  extract  will  contain,  along  with  the  fat,  any  other  ether-sol- 
uble substances  which  were  present  in  the  food,  and  may  con- 
tain substances  which,  while  not  appreciably  soluble  in  ether 
alone,  are  dissolved  by  the  mixture  of  ether  and  fat.  It  is  there- 
fore somewhat  more  accurate  to  speak  of  the  material  extracted 
by  ether  as  "  ether  extract  "  rather  than  as  "fat,"  and  it  will 
be  found  so  designated  in  some  statements  of  analytical  results. 
In  most  human  foods  —  at  least  those  which  are  important  as 


FATS  AND  LIPOIDS  21 

sources  of  fat  —  the  constituents  of  the  ether  extract  other 
than  true  fat  are  for  the  most  part  fat-like  substances  and  we 
shall  therefore  be  sufficiently  accurate  in  most  cases  if  we  desig- 
nate the  material  extracted  by  ether  by  the  simple  term  "  fat," 
remembering,  however,  that  we  may  thus  include  along  with 
the  glycerides  (and  any  free  fatty  acids  which  may  be  present) 
small  amounts  oi  fat-like  substances  or  lipoids,  and  of  fat-soluble 
or  other  ether-soluble  matter. 

rrhe  food  fats  of  commerce  have  been  separated  from  the 
materials  in  which  they  naturally  occurred  not  by  solvents  as 
above  described  but  by  mechanical  means  such  as  churning 
(butter)  or  pressing  (olive  or  cottonseed  oil)  but  even  in  this 
case  the  naturally  occurring  fat-soluble  substances  will  still 
remain  dissolved  in  the  separated  fat.  Recent  investigations 
indicate  that  these  fat-Hke  and  fat-soluble  substances,  although 
occurring  only  in  small  quantities,  may  have  very  important 
functions  in  nutrition.  We  shall  have  occasion  to  study  them 
in  that  connection  later. 

'The  actual  glycerides  of  any  common  natural  fat,  with  the 
exception  of  butter,  would  if  obtained  absolutely  pure  be  color- 
less, tasteless,  and  odorless.  The  colors,  tastes,  and  odors  of 
fats  are  therefore  ordinarily  due  to  substances  present  in  small 
amount  which  might  be  removed  by  refining  processes.  All 
of  the  quantitative  differences  among  the  fats  are  to  be  accounted 
for  by  the  kinds  and  the  amounts  of  the  fatty  acids  which  enter 
into  the  composition  of  the  glycerides. 

Fatty  Acids 

The  greater  number  of  the  fatty  acids  belong  to  a  few  homol- 
.  ogous  series.     The  series  to  which  stearic  acid  belongs  may  be 
represented  by  the  general  formula,  CnH2n02,  and  is  made  up 
of  homologues  of  acetic  acid.    The  principal  members  of  physi- 
ological importance  are  as  follows: 


22  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Acids  of  the  Series  C„H2n02 

Butyric  acid  (C4H8O2)  occurs  as-glyceride  to  the  extent  of 
about  5  to  6  per  cent  in  butter  and  in  very  small  quantities  in 
a  few  other  fats. 

Caproic  acid  (C6H12O2)  is  obtained  from  goat  and  cow  butter 
and  coconut  fat. 

Caprylic  acid  (C8H16O2)  is,  obtained  from  coconut  oil,  butter, 
and  human  fat. 

Capric  acid  (C10H20O2)  is  obtained  from  coconut  oil,  butter, 
and  the  fat  of  the  spice  bush. 

Laurie  acid  (C12H24O2)  occurs  abundantly  as  glyceride  in 
the  fat  of  the  seeds  of  the  spice  bush,  and  in  smaller  propor- 
tions in  butter,  coconut  fat,  palm  oil,  and  some  other  vege- 
table oils. 

Myristic  acid  (C14H28O2)  is  obtained  from  nutmeg  butter, 
coconut  oil,  butter,  lard,  and  many  other  fats,  as  well  as  from 
spermaceti  and  wool  wax. 

Palmitic  acid  (C16H32O2)  occurs  abundantly  in  a  great  va- 
riety of  fats,  both  animal  and  vegetable,  including  many 
fatty  oils,  and  also  in  several  waxes,  including  spermaceti  and 
beeswax. 

Stearic  acid  (C18H36O2)  is  found  in  most  fats,  occurring  more 
abundantly  in  the  solid  fats  and  especially  in  those  having  high 
melting  points. 

Butyric  acid  is  a  mobile  hquid,  mixing  in  all  proportions  with 
water,  alcohol,  and  ether,  boiling  without  decomposition,  and 
readily  volatile  with  steam.  With  increasing  molecular  weight 
the  acids  of  this  series  regularly  show  increasing  boihng  or 
melting  points,  decreasing  solubihty,  and  loss  of  volatiHty  with 
steam.  For  ordinary  temperatures  the  dividing  Hne  between 
liquids  and  solids  falls  at  about  capric  acid.  Stearic  acid  is  a 
crystalline  soHd,  insoluble  in  water,  and  only  moderately  soluble 
in  alcohol  and  ether. 


FATS  AND  LIPOIDS  23 

Acids  of  the  Series  CnH2n-202 

These  are  unsaturated  compounds.  Each  molecule  contains 
one  ethylene  linkage  or  "  double  bond,"  and  can  take  up  by 
addition  two  atoms  of  halogen  to  form  a  saturated  compound.* 
These  unsaturated  acids  have,  as  a  rule,  much  lower  melting 
points  than  the  saturated  acids  containing  the  same  number 
of  carbon  atoms.  The  glycerides  show  correspondingly  lower 
melting  points  than  those  of  the  saturated  fatty  acids  and  are 
therefore  found  more  largely  in  the  soft  fats  and  the  fatty  oils. 
Such  soft  fats  or  fatty  oils  can  be  hardened  to  any  desired  con- 
sistency (up  to  that  of  stearin)  by  hydrogenation,  which  changes 
the  unsaturated  fatty  acid  radicles  into  the  corresponding 
members  of  the  saturated  series.  In  recent  years  this  process 
has  been  exploited  commercially  and  large  quantities  of  refined 
cottonseed  oil  are  now  hydrogenated  to  the  consistency  of  lard 
and  sold  under  trade  names  as  lard  substitutes.  Other  oils 
are  also  hardened  by  hydrogenation. 

Fhycetoleic  acid  (C16H30O2)  is  obtained  from  seal  oil  and  sperm 
oil ;  an  isomeric  acid,  hypogceic,  occurs  in  peanut  oil. 

Oleic  acid  (C18H34O2)  occurs  as  glyceride  in  nearly  all  fats  and 
fatty  oils  and  is  much  the  most  important  member  of  the 
series.  Many  of  the  typical  oils  of  both  animal  and  vegetable 
origin,  such  as  lard  oil  and  olive  oil,  consist  mainly  of  olein. 

Erucic  acid  (C22H42O2)  is  obtained  from  rape  seed  and  mustard 
seed  oils,  and  is  not  found  in  animal  fats  except  when  oils  which 
contain  this  acid  have  been  fed  to  the  animal. 

The  gradual  change  in  physical  properties  with  increasing 
molecular  weight  which  is  noticeable  in  the  stearic  acid  series 
is  not  apparent  in  this  series,  probably  because  the  known  acids 

*  The  relative  number  of  double  bonds  is  measured  analytically  by  determining 
the  percentage  of  iodine  which  the  fat  or  fatty  acid  will  absorb.  Thus  pure  oleic 
acid  (mol.  wt.  282)  absorbs  2  atoms  of  iodine,  giving  an  "iodine  number"  of  90; 
pure  linoleic  acid  would  absorb  4  atoms  of  iodine  to  the  molecule,  giving  an  "iodine 
number"  about  twice  as  great. 


24  CHEMISTRY  OF  POOD  AND  NUTRITION 

of  the  series  differ  as  regards  the  position  of  the  double  bond  and 
are  therefore  not  strictly  homologous. 

Other  Unsaturated  Fatty  Acids 

Acids  of  the  series  CnH2n-402,  C„H2n-602,  and  CnH2n-802 
have  been  found  to  occur  as  glycerides  in  some  of  the  fats. 
Linoleic  acid,  C18H32O2,  and  linolenic  acid,  C18H30O2,  are  the 
best  known  of  these  acids.  They  are  found  abundantly  in 
linseed  oil  and  in  others  of  the  so-called  "  drying  oils,"  which  on 
account  of  the  affinity  for  oxygen  of  their  highly  unsaturated 
glycerides  are  gradually  oxidized  to  solids  on  exposure  to  the 
air.  Fatty  acids  having  the  same  number  of  double  bonds,  but 
not  the  same  property  of  oxidizing  to  hard,  solid  films  are  found 
in  fatty  oils  of  animal  origin,  especially  those  obtained  from 
marine  animals  and  from  fishes.  Since  the  acids  of  this  series 
have  still  lower  melting  points  than  the  corresponding  acids 
of  the  oleic  series,  and  since  the  physical  properties  of  the  glyc- 
erides follow  those  of  the  fatty  acids  which  they  contain,  a  fat 
containing  an  acid  isomeric  with  linoleic  or  Hnolenic  acid  will 
be  more  fluid  at  any  given  temperature  than  one  containing 
oleic  acid  in  the  same  proportion.  Hence,  it  is  apparent  that 
glycerides  of  the  highly  unsaturated  and  more  fluid  acids  are 
physiologically  adapted  to  the  cold-blooded  animals,  and  it  is 
found  that  they  are  especially  abundant  in  fish  fat ;  the  acids 
of  the  series  CnH2n-802  have  been  obtained  as  yet  only  from 
fish  oils. 

P  "  Simple  "  and  "  Mixed  "  Triglycerides 

V  Triglycerides  in  which  the  three  fatty  acid  radicles  are  of  the 
same  kind  are  known  as  simple  triglycerides.  Tristearin,  triolein, 
tripalmitin,  etc.,  are  examples  of  simple  triglycerides.  A  mixed 
triglyceride  is  one  in  which  the  three  fatty  acid  radicles  are  not 
all  of  the  same  kind.  For  example,  distearo-olein  (having  two 
radicles  of  stearic  and  one  of  oleic  acid),  dioleo-palmitin  (having 


FATS  AND   LIPOIDS  25 

two  of  oleic  and  one  of  palmitic),  or  stearo-oleo-palmitin  (hav- 
ing one  radicle  each  of  stearic,  oleic,  and  palmitic  acids),  is 
each  a  mixed  triglyceride. 

It  is  evident  from  the  chemical  structure  of  glycerol  that 
there  can  be  only  one  simple  triglyceride  of  any  given  fatty 
acid  but  that  with  two  fatty  acid  radicles  alike  (R2)  and  one  dif- 
ferent (Ri)  the  triglyceride  may  have  either  of  the  following 
forms : 

H  H 

I  I 

HC-OR2  HC-ORi 

I  I 

HC-ORi  HC-OR2 

I  I 

HC-OR2  HC-OR2 

I  I 

H  H 

That  is,  the  two  radicles  of  the  same  kind  may  be  on  the  ter- 
minal carbons  or  may  be  adjacent.  It  will  be  noted  that  the  two 
substances  here  represented  have  exactly  the  same  compo- 
sition, but  different  constitution. 

If  now  the  triglyceride  contains  one  each  of  three  different 
acid  radicles  (Ri,  R2,  R3)  there  are  plainly  three  possible  forms : 

H  H  H 

I  I  I 

HC-ORi  HC-OR2  HC-ORi 

I  I  I 

HC-OR2  HC-ORi  HC-OR3 

I  I  I 

HC-OR3  HC-OR3  HC-OR2 

I  I  I 

H  H  H 

Each  of  these  three  substances  has  exactly  the  same  com- 
position, though  the  constitution  is  different  for  each. 


26  CHEMISTRY  OF  FOOD   AND  NUTRITION 

It  should  be  noted  that  these  five  formulae  represent  types  of 
structure  and  that  the  actual  number  of  triglycerides  possible 
from  three  fatty  acid  radicles  is  greater  since  we  may  have  sub- 
stances corresponding  to  either  of  the  first  two  in  which  R3 
replaces  either  Ri  or  R2 ;  and  it  is  plain  that  as  the  number  of 
fatty  acids  is  increased  beyond  three  the  number  qf  possible 
mixed  triglycerides  increases  very  rapidly  so  that  with  the  large 
number  of  fatty  acids  which  are  now  known  to  be  of  fairly  com- 
mon occurrence  in  fats  the  possible  number  of  mixed  triglycer- 
ides must  be  almost  unlimited.  The  simple  triglycerides  cor- 
responding to  the  common  fatty  acids  are  all  known,  but 
naturally  not  all  of  the  practically  innumerable  possible  mixed 
triglycerides  have  been  separated  or  prepared. 

Berthelot  in  1869  suggested  that  fats  probably  contain 
mixed  glycerides  and  in  1889  Blyth  and  Robertson  reported  a 
palmito-stearo-olein  in  butter,  but  it  is  only  since  Kreis  and 
Hafner  (1903)  described  the  preparation  of  palmito-distearin 
from  beef  tallow  and  Bomer  (1909)  separated  stearo-dipalmitin 
from  mutton  tallow  and  palmito-distearin  from  lard  that  the 
widespread  occurrence  of  mixed  glycerides  in  the  familiar  fats 
has  been  generally  accepted. 

Among  the  other  mixed  glycerides  reported  as  having  been 
isolated  from  natural  fats  are: 

Myristo-palmito-olein  in  cacao  butter  (Klimont,  1902), 
dipalmito-olein  and  stearo-palmito-olein  in  tallow  (Hansen,  1902), 
distearo-olein  in  cacao  butter  (Fritzweiler,  1903)  and  in  Borneo 
tallow  (Klimont,  1905),  stearo-diolein  in  human  fat  (Partheil 
and  Ferie,  1903). 

The  fact  long  known  to  analysts  that  fats  too  nearly  identical 
in  composition  to  be  distinguished  by  chemical  analysis  may  still 
show  differences  in  crystalHne  structure  under  the  microscope 
is  now  explained  as  due  to  the  presence  of  different  mixed  tri- 
glycerides containing  the  same  fatty  acid  radicles.  Thus  beef 
fat  rendered  at  such  a  temperature  as  to  contain  the  glycer- 


FATS  AND  LIPOIDS  27 

ides  of  stearic,  palmitic,  and  oleic  acids  in  practically  the 
same  proportions  as  in  lard  still  differs  so  constantly  from  lard 
in  its  microscopic  appearance  as  to  indicate  the  presence  of  dis- 
tinct chemical  substances  and  has  now  been  shown  to  contain 
different  mixed  triglycerides. 

The  fact  that  tributyrin  has  an  intensely  bitter  taste  makes 
it  seem  probable  that  none  of  this  substance  occurs  in  butter 
but  rather  that  the  butyric  acid  in  butter  fat  is  in  the  form  of 
mixed  glycerides.  Probably  mixed  glycerides  are  as  abundant 
as  simple  glycerides  in  natural  fats. 

Formation  and  Composition  of  Natural  Fats 

Fats  are  formed  both  in  plants  and  in  animals.  The  con- 
ditions which  determine  fat  formation,  and  the  character  of  the 
fat  formed  in  different  species  and  under  different  conditions, 
are  better  known  than  the  chemical  steps  involved  in  the 
process.  It  is  hardly  necessary  to  mention  the  fact  that  the 
true  fats  are  composed  of  the  same  three  chemical  elements  of 
which  the  carbohydrates  are  composed  (carbon,  hydrogen, 
and  oxygen)  and  that  since  the  fats  contain  less  oxygen  and 
more  carbon  and  hydrogen  than  the  carbohydrates,  they  con- 
stitute a  more  concentrated  form  of  fuel  or  a  more  compact 
and  lighter  medium  for  the  storage  of  energy  for  future  use^ 
The  question  therefore  presents  itself  whether  either  the  plant 
or  the  animal  organism  (or  both)  has  the  power  to  change  car- 
bohydrate material  into  fat. 

Formation  of  Fat  from  Carbohydrate 

In  plants  there  are  many  indications  of  the  formation  of  fat 
from  carbohydrate,  as  when  decrease  of  starch  and  increase  of 
fat  go  on  simultaneously  in  a  ripening  seed,  or  when  sugars  are 
found  to  be  constantly  brought  to  a  tissue  in  which  fat  is  form- 
ing and  there  disappear  as  the  formation  of  fat  progresses.    It 


28  CHEMISTRY  OF   FOOD  AND  NUTRITION 

is  probably  because  no  one  has  doubted  the  formation  of  fat 
from  carbohydrate  in  plants  that  the  process  has  not  been  more 
rigorously  investigated. 

In  animals  it  is  certain  that  fat  may  be  formed  from  carbo- 
hydrate. From  the  standpoint  of  our  present  knowledge  it 
would  seem  that  the  readiness  with  which  farm  animals  are 
fattened  on  essentially  carbohydrate  food  should  have  been 
sufi&cient  to  convince  early  observers ;  but  this  evidence  appears 
to  have  been  overlooked  formerly  because  of  the  idea,  for  a 
long  time  prevalent,  that  simpler  substances  are  built  up  into 
more  complex  compounds  only  in  the  plant,  and  not  in  the  ani- 
mal organism.  In  recent  years  it  has  become  necessary  to  aban- 
don this  latter  assumption  completely,  and  there  is  now  abun- 
dant evidence  that  the  animal  body  synthesizes  fat  from 
carbohydrate. 

The  most  obvious  method  of  demonstrating  the  conversion 
of  carbohydrate  into  fat  is  that  followed  by  Lawes  and  Gil- 
bert. Several  pigs  of  the  same  litter  and  of  similar  size  were 
selected;  some  were  killed  and  analyzed  as  ''  controls,"  while 
the  others  were  fed  on  known  rations  and  later  weighed,  killed, 
and  analyzed  to  determine  the  kinds  and  amounts  of  material 
stored  in  the  body.  In  several  cases  the  amounts  of  fat  stored 
during  such  feeding  trials  were  found  to  have  been  much  larger 
than  could  be  accounted  for  by  all  of  the  fat  and  protein  fed,  so 
that  at  least  a  part,  and  in  some  cases  the  greater  part,  of  the 
body  fat  must  have  been  formed  from  the  carbohydrate  of  the 
food.  Many  similar  experiments  have  been  made,  and  the 
transformation  of  carbohydrate  into  fat  has  been  demonstrated 
by  this  method  in  carnivorous  as  well  as  herbivorous  animals. 

It  has  also  been  shown  that  carbohydrates  contribute  to  the 
production  of  milk  fat.  Jordan  and  Jenter.  kept  a  milch  cow 
for  fifty-nine  days  upon  food  from  which  nearly  all  of  the  fat 
had  been  extracted.  During  this  period  about  twice  as  much 
milk  fat  was  produced  as  could  be  accounted  for  by  the  total 


FATS  AND  LIPOIDS  29 

fat  and  protein  of  the  food,  and  in  addition  the  cow  gained  in 
weight  and  her  appearance  showed  that  she  had  more  body  fat 
at  the  end  than  at  the  beginning  of  the  experiment. 

Instead  of  determining  directly  the  fat  formed  in  the  animal 
fed  on  carbohydrate,  the  production  of  fat  from  carbohydrate 
may  be  demonstrated  by  keeping  the  animal  experimented  upon 
in  a  respiration  chamber  so  arranged  that  the  total  carbon  given 
off  from  the  body  may  be  determined  and  compared  with  the 
total  carbon  of  the  food.  If  in  such  a  case  the  body  is  found 
to  store  more  carbon  than  it  could  store  as  carbohydrate  or  pro- 
tein, it  is  safe  to  infer  that  at  least  the  excess  of  stored  carbon 
is  held  in  the  form  of  fat.  Many  such  experiments  upon  dogs, 
geese,  and  swine  have  shown  storage  of  carbon  very  much 
greater  than  could  be  accounted  for  on  any  other  assumption 
than  that  a  part  of  the  carbon  of  the  carbohydrates  eaten  re- 
mained in  the  body  in  the  form  of  fat. 

Further  evidence  of  the  transformation  of  carbohydrate  into 
fat  in  the  animal  body  is  obtained  from  the  "  respiratory 
quotient."  The  discussion  of  the  quotient  and  the  significance 
of  the  information  which  it  furnishes,  as  also  the  study  of  the 
chemical  steps  through  which  the  transformation  of  carbohydrate 
into  fat  may  take  place,  will  be  taken  up  in  connection  with  the 
general  study  of  the  fate  of  the  foodstuffs  in  metaboHsm  (Chap- 
ter V). 

Composition  and  Properties  of  Animal  Fat 

Just  as  we  found  that  the  character  of  the  fat  of  the  cold- 
blooded animals  is  adapted  to  the  maintenance  of  a  fluid  or 
plastic  consistency  at  the  low  temperature  to  which  it  is  ex- 
posed, so  to  a  less  degree  ^the  character  of  the  fat  of  warm- 
blooded animals  appears  to  vary  with  its  position  in  the  body 
and  with  the  temperature  to  which  the  body  is  subjected  during 
the  time  that  the  fat  is  in  process  of  formation]^  Thus  Hen- 
riques  and  Hansen  concluded  from  experiments  with  pigs  that 


30 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


the  thick  layer  of  subcutaneous  fat  on  the  back,  where  it  was 
not  thoroughly  warmed  by  the  blood  and  therefore  had  an  aver- 
age temperature  considerably  below  that  of  the  interior  of  the 
body,  was  richer  in  unsaturated  compounds  (olein,  etc.)  and 
had  a  lower  melting  point  than  the  fat  of  the  body  as  a  whole ; 
while  the  fat  from  animals  which  had  been  grown  in  a  warm 
room,  or  which  had  been  heavily  jacketed  so  that  the  skin  was 
not  exposed  to  cold  air,  contained  near  the  skin  fat  of  more 
nearly  the  same  composition  as  in  the  interior  of  the  body. 

Moulton  and  Trowbridge  have  observed  that  the  fat  in  beef 
animals  becomes  richer  in  olein  and  therefore  softer  with  age, 
with  fatness,  and  with  nearness  to  the  surface  of  the  body. 

Usually,  however/  the  nature  of  the  fat  found  in  the  body  is 
more  or  less  characteristic  of  each  species  or  group  of  closely 
related  species.;  Herbivora  contain  as  a  rule  harder  fats  than 
carnivora,  land  animals  have  harder  fats  than  marine  animals, 
and  all  warm-blooded  animals  have  fats  which  are  decidedly 
harder  than  those  found  in  fishes.  The  fats  of  different  mam- 
mals were  investigated  by  Schulze  and  Reineke,  whose  results  * 
showed  httle  variation  from  an  average  of  carbon,  76.5  per  cent ; 
hydrogen,  12  per  cent;  oxygen,  11.5  per  cent,  as  may  be  seen 
from  the  following : 


Kind  of  Fat 

Carbon 

Hydrogen 

Oxygen 

Human  fat  f 

Beef  fat 

Mutton  fat 

Pork  fat 

76.62 
76.50 
76.61 
76.54 

11.94 
II. 91 
12.03 
11.94 

11.44 
11.59 
11.36 
11.52 

The  foregoing  statements  refer  to  the  fat  of  the  adipose  tis- 
sues.    In  the  fat  extracted  from  the  liver,  kidney,  and  heart, 

*  Armsby's  Principles  of  Animal  Nutrition,  page  6i. 

t  Benedict  and  Osterberg  {American  Journal  of  Physiology,  Vol.  4,  page  69) 
found  in  8  samples  of  human  fat  an  average  of  76.08  per  cent  carbon  and  11.78 
per  cent  hydrogen. 


FATS  AND  LIPOIDS  3 1 

Hartley*  finds  fatty  acids  of  the  series  C„H2»_402,  CaH2„-602, 
and  possibly  C„H2,»_802. 

A  possible  explanation  of  this  difference  between  the  fat  of 
the  adipose  tissues  and  of  the  actively  functioning  organs  is  to 
be  found  in  the  greater  reactivity  of  the  unsaturated  acid  radi- 
cles. )  The  saturated  fatty  acid  radicles  are  relatively  stable 
and  inert ;  and  when  the  glycerides  of  such  acids  are  deposited 
in  the  inactive  adipose  tissues,  the  fats  may  remain  unaltered 
for  a  long  time  and  accumulate  in  considerable  quantities. 
The  unsaturated  fatt}''  acid  radicles  are  less  stable  and  more 
readily  acted  upon  and  broken  up.  This  is  consistent  with  the 
fact  that  we  find  them  more  abundantly  in  fats  of  the  organs 
in  which  metaboHsm  is  more  active  and  has  led  to  the  view  that 
the  desaturation  of  fatty  acid  radicles  by  the  active  organs  of 
the  body  may  be  an  important  preliminary  to  the  metabolism 
of  the  fat.  On  the  other  hand,  the  formation  of  unsaturated 
fatty  acid  radicles  such  as  oleic  and  linoleic  does  not,  according 
to  our  present  knowledge,  seem  essential  to  the  "  /8-oxidation 
theory  "  which  is  now  generally  held  as  most  probably  repre- 
senting the  main  course  of  fatty  acid  metaboHsm  (Chapter  V). 
It  is  therefore  entirely  possible  that  the  highly  unsaturated 
fatty  acids  found,  for  example,  in  the  liver,  may  be  present  as 
constituents  of  the  protoplasm  of  these  cells,  essential  to  the 
properties  which  enable  them  to  carry  out  some  of  their  func- 
tions but  not  necessarily  connected  with  the  metabolism  of  fat 
itself. 

Butter  fat  differs  from  body  fat  in  containing  fatty  acids  of 
lower  molecular  weight  (particularly  butyric  acid,  which  is 
fairly  characteristic  of  butter),  and  so  shows  a  higher  percent- 
age of  oxygen  and  lower  percentages  of  carbon  and  hydrogen. 
The  most  abundant  acids  of  butter  fat  are,  however,  palmitic, 
oleic,  and  myristic,  and  the  ultimate  composition  is  not  very 
greatly  different  from  that  of  body  fats.X  A  sample  of  butter 

*  Journal  of  Physiology,  Vol.  36,  page  17. 


32  CHEMISTRY  OF  FOOD  AND  NUTRITION 

fat  analyzed  by  Browne  *  showed  75.17  per  cent  carbon,  11.72 
per  cent  hydrogen,  and  13. 11  per  cent  oxygen. 


Storage  of  Food  Fat  in  the  Body 

In  discussing  the  formation  of  body  fat  from  carbohydrate  it 
was  shown  that(of ten  the  greater  part  of  the  fat  stored  is  manu- 
factured in  the  body  from  carbohydrate.  So  striking  were  the 
results  of  some  of  the  experiments  demonstrating  the  synthesis 
of  fat  from  carbohydrate,  that  physiologists  came  to  question 
for  a  time  whether  any  of  the  fat  deposited  in  the  tissues  comes 
from  the  fat  of  the  food.  Abundant  evidence  that  food  fats 
may  be  directly  deposited  in  the  body  has  been  obtained  by 
feeding  characteristic  fats  to  dogs  and  showing  that  these  fats 
can  afterwards  be  recognized  in  the  tissues  of  the  animals. 
Experiments  of  this  kind  have  been  made,  using  Unseed  oil, 
rapeseed  oil,  or  mutton  tallow,  any  of  which  is  easily  distinguish- 
able by  its  chemical  and  physical  properties  from  the  fat  nor- 
mally found  in  the  body  of  the  dog.  For  example,  Munk  starved 
a  dog  for  19  days,  and  then  for  14  days  fed  a  mixture  of  the 
fatty  acids  obtained  from  mutton  tallow,  as  a  consequence  of 
which  about  one  half  of  the  weight  lost  by  fasting  was  regained. 
The  dog  was  then  killed  and  yielded  on  dissection  iioo  grams  of 
fat  melting  at  40°,  which  is  about  the  melting  point  of  mutton 
tallow,  whereas  normal  dog  fat  melts  at  about  20°.  In  another 
experiment  by  Munk  rape  oil  was  fed  and  the  fat  obtained  from 
the  dog  was  found  to  contain  82.4  per  cent  of  oleic  and  erucic 
acids  and  12.3  per  cent  of  soUd  acids,  whereas  normal  dog  fat 
had  only  65.8  per  cent  oleic,  no  erucic,  and  28.8  per  cent  of 
soHd  fatty  acids. 

The  occurrence  in  the  body  fat  of  properties  usually  char- 
acteristic of  some  particular  fat  which  has  been  fed  is  now  very 
well  tnown  and  is  recognized  in  establishing  standards  of  purity 

*  Journal  of  the  American  Chemical  Society,  Vol.  21,  page  823  (1899). 


FATS  AND  LIPOIDS  33 

for  fats  of  animal  origin.  Thus,  the  lard  obtained  from  swine 
which  have  been  fed  cottonseed  meal  shows  the  characteristic 
color  reactions  of  cottonseed  oil,  and  more  elaborate  tests 
must  be  made  in  order  to  determine  whether  cottonseed  fat  has 
actually  been  mixed  with  the  lard. 

European  food  oflGicials  sought  to  establish  an  easy  method 
of  distinguishing  between  butter  and  its  substitutes  by  requiring 
manufacturers  of  any  butter  substitute  to  use  a  certain  pro- 
portion of  sesame  oil  in  the  preparation,  sesame  oil  having  a 
characteristic  color  reaction  which  can  be  very  easily  demon- 
strated without  the  use  of  laboratory  facihties.  It  was  found, 
however,  that  the  same  sesame  oil  reaction  might  be  exhibited 
by  a  perfectly  pure  butter  fat  from  cows  which  had  been  fed 
upon  sesame  meal. 

Evidence  of  the  formation  of  body  fat  from  food  fat  has  also 
been  obtained  by  experiments  upon  the  total  amount  of  fat 
formed  in  the  body  when  the  amount  and  composition  of  the 
food  eaten  was  accurately  known.  Hoffmann  starved  a  dog 
until  its  weight  had  decreased  from  26  to  16  kilograms,  so  that 
it  must  have  been  almost  devoid  of  fat.  He  then  fed  small 
amounts  of  meat  and  large  amounts  of  fat  for  five  days,  after 
which  the  dog  was  killed  and  analyzed.  The  body  contained 
1353  grams  of  fat,  of  which  not  over  131  grams  could  have 
come  from  proteins,  and  only  a  few  grams  at  most  from  the 
small  amount  of  carbohydrates  in  the  meat  fed,  so  that  about 
nine  tenths  of  the  fat  which  the  animal  had  laid  on  must  have 
come  from  the  fat  of  the  food. 

Thus  there  is  abundant  experimental  evidence  that  MDoth 
the  carbohydrate  and  the  fat  of  the  food  may  serve  as  sources 
of  body  fat.  In  a  later  chapter  it  will  be  shown  that  protein 
also  may  contribute  to  the  production  of  fat  in  the  body. 

A  question  naturally  arises  as  to  how,  if  proteins,  fats,  and 
carbohydrates  of  food  may  all  contribute  to  the  production  of 
body  fat,  the  nature  of  the  fat  can  still  be  to  any  significant  de- 


34  CHEMISTRY   OF   FOOD  AND  NUTRITION 

gree  characteristic  of  the  species  in  which  it  is  found.  A  partial 
explanation  appears  to  be  furnished  by  the  recent  work  of 
Bloor,  who  finds  that  when  the  fat  of  the  food  has  been  spUt 
to  glycerol  and  fatty  acids  in  the  course  of  digestion  and  these 
digestion  products  are  taken  up  and  resynthesized  to  fat  in  the 
intestinal  wall,  there  may  go  into  the  resynthesized  fat  not  only 
the  fatty  acid  radicles  of  the  food  fat  but  also  fatty  acid,  radicles 
formed  in  the  body.  These  latter,  entering  into  the  consti- 
tution of  the  absorbed  fat,  tend  to  give  it  some  of  the  proper- 
ties characteristic  of  the  species  while  at  the  same  time  some  of 
the  characteristics  of  the  food  fat  may  be  retained.  Thus  when 
a  dog  is  fattened  by  feeding  mutton  tallow  which  contains  more 
stearin  and  less  olein  than  ordinary  dog  fat  the  organism  may, 
if  the  fattening  is  gradual,  furnish  enough  oleic  acid  radicles  to 
bring  the  resynthesized  fat  to  the  consistency  ordinarily  found 
in  dog  fat,  or  if  the  fattening  is  more  rapid  the  oleic  acid  radicles 
may  not  be  supplied  at  a  sufficiently  rapid  rate  to  yield  this 
result  and  the  dog  will  then  lay  on  fat  of  a  character  somewhere 
between  that  of  mutton  tallow  and  ordinary  dog  fat,  the  in- 
fluence of  the  food  fat  upon  the  character  of  the  stored  fat  being 
more  pronounced  the  more  rapidly  the  fattening  is  carried  out. 
It  will  be  noted  that,  even  if  the  fatty  acid  radicles  synthesized 
in  the  body  are  built  into  the  absorbed  fat  to  such  an  extent  as 
to  bring  its  consistency  and  other  physical  properties  to  what  is 
characteristic  for  the  species,  yet  such  body  fat  may  still  con- 
tain some  radicles  of  fatty  acids  characteristic  of  the  experi- 
mental food  and  not  ordinarily  found  in  the  fat  of  the  animal, 
as  in  the  case  of  erucic  acid  in  the  experiment  cited  above 
\j'  (page  32). 

Fats  and  Lipoids  as  Body  Constituents 

From  what  has  been  stated  above,\fat  is  seen  to  be  a  form 
of  reserve  fuel  to  which  any  of  the  organic  foodstuffs  may 
contribute  (see  also  the  discussion  of  fate  of  the  foodstuffs  in 


FATS  AND   LIPOIDS  35 

Chapter  V).  It  is  as  reserve  fuel  that  the  large  deposits  of  body 
fat  are  chiefly  significant,  but  it  should  not  be  forgotten  that 
even  this  ''  depot  fat  "  may  function  as  a  protection  to  the  body 
from  mechanical  injury  and  toojw)id  a  loss  of  heat  when  exposed 
to  cold,  and  as  a  packing  and^pport  to  the  visceral  organs, 
particularly  the  kidneys.  In  recent  years  it  has  come  to  be  rec- 
ognized^hat  modified  fats  and  fat-like^ubstances  (lipoids)  are 
essential  constituents  of  body  tissues,  ^lus  cell  membranes  are 
not  simply  walls  of  protein  matter  but  probably  are  composed  of 
both  proteins  and  lipoids  of  different  kinds  and  in  varying  pro- 
portions, and  protoplasm  is  to  be  thought  of  as  an  emulsion  of 
proteins  and  lipoids  rather  than  as  a  jelly  of  proteins  alone. 

Taylor,  writing  in  191 2,  says:  *  "  Fat  plays  two  roles  within 
the  body.  Fat  represents  the  ultimate  form  of  the  storage  of 
fuel,  and  the  depot  fats  are  quite  the  most  inert  and  dead  of 
any  of  the  body  structures.  On  the  other  hand,  fats  joined 
with  protein  and  in  complex  combinations  of  still  unknown 
composition,  represent  the  most  essential  structures  in  cellular 
protoplasm,  cell  membranes,  and  in  the  central  nervous  system. 
The  subjects  of  fat  in  its  cellulometabolic  relations  and  fat  in 
the  energy  metabolism  are  almost  as  distinct  as  though  different 
substances  were  under  consideration.  Our  information  on  the 
two  subjects  is  not  equal;  we  know  much  concerning  fat  as 
fuel ;   we  know  little  concerning  fat  in  cellular  structure." 

Mathews,  in  1915,!  writes:  ''It  will  be  recalled  that  all 
living  matter  contains  a  larger  or  smaller  amount  of  organic 
substances  which  are  soluble  in  alcohol,  ether,  and  other  fat 
solvents.  These  substances  help  to  give  to  protoplasm  its 
properties  of  containing  large  amounts  of  water  but  not  dis- 
solving ;  and  also  the  power  of  taking  up  readily  and  in  large 
amounts  chloroform,  ether,  and  other  substances  soluble  in  fats 
but  not  readily  soluble  in  water.  They  are  among  the  funda- 
mental and  ever-present  constituents  of  living  matter." 

*  Digestion  and  Metabolism,  page  342.  t  Physiological  Chemistry,  page  61. 


36  CHEMISTRY  OF  FOOD   AND  NUTRITION 

Following  the  suggestion  of  Gies,*  Mathews  includes  all 
such  substances  under  the  group  name  of  lipins  (from  the  Greek, 
lipos,  fat)  which  is  thus  made  to  cover  both  the  true  fats  and 
all  fat-Hke  or  lipoid  substances^  According  to  Mathews'  classi- 
fication based  on  that  propo^  by  Gies,  the  term  "lipins" 
covers :  "  Alcohol-ether  soluble  constituents  of  protoplasm  hav- 
ing a  greasy  feel  and  insoluble  in  water."  These  are  divided 
into  nine  groups  as  folrows : 

1.  Fats  and  fatty  acids,  the  term  "fat"  being  here  confined  to  those 
neutral  glycerides  which  are  solid  at  20°  C. 

2.  Fatty  oils  (Uquid  at  2o°C.)  including  (i)  drying  oils  such  as  linseed 
oil,  (2)  semidrying  oils  such  as  cottonseed  oil,  (3)  non-drying  oils  such  as 
olive  oil. 

3.  Essential  oils.  Volatile,  generally  odoriferous,  oil  substances  of  varied 
chemical  nature. 

4.  Waxes.  Esters  of  fatty  acids  with  monatomic  alcohols  of  high  molec- 
ular weight  such  as  the  sterols. 

5.  Sterols.  Alcohols,  generally  of  terpene  group,  soluble  at  ordinary 
temperatures.     Cholesterol,  phytosterol,  etc. 

.     6.   Phospholipins.     Phosphatids.    Fatty  substances,  yielding  on  hydroly- 
sis phosphoric  acid  and  fatty  acids  (as  well  as  glycerol) .     Lecithin,  cephalin. 

7.  Glycolipins.  Fatty  substances  free  from  phosphorus,  yielding  on 
hydrolysis  fatty  acids  and  a  carbohydrate.     Cerebron,  phrenosin. 

8.  Sulpholipins.  Fatty  substances,  yielding  on  hydrolysis  fatty  acids 
and  sulphuric  acid.     Sulphatide  of  brain. 

9.  Aminolipins.  Fatty  substances,  free  from  phosphorus,  which  contain 
amino  nitrogen. 

Mathews  remarks :  "  While  the  group  of  Upins  contains  such 
widely  different  chemical  substances  as  the  aromatic  essential 
oils,  like  clove  oil,  the  true  neutral  fats,  like  mutton  tallow,  the 
sterols,  which  are  aromatic  alcohols,  and  the  phosphatids,  or 
phospholipins,  which  contain  large  amounts  of  phosphoric 
acid,  the  members  of  the  group  all  possess  two  or  three  proper- 
ties by  virtue  of  which  they  are  called  lipins.  These  properties  are 
their  greasy  or  fat-like  feel,  their  solubility  in  chloroform  and  fat 

*  A  more  elaborate  classification  of  the  lipins  is  suggested  by  Gies  and^  Rosen- 
bloom  in  the  article  cited  at  the  end  of  this  chapter. 


FATS  AND  LIPOIDS  37 

solvents,  and  their  insolubility  in  water.  They  constitute,  then, 
a  very  heterogeneous  group,  chemically  and  physiologically." 

We  have  therefore,  in  the  large  heterogeneous  group  of  sub- 
stances called  lipins:  (i)  true  fatty  substances  —  fats,  fatty 
oils,  fatty  acids,  (2)  fat-Uke  or  lipoid  substances — some  of  these 
latter  (Hke  lecithin  and  other  phospholipins)  being  closely 
related  to  the  fats  both  chemically  and  biologically,  others 
(Hke  the  sterols)  showing  little  direct  chemical  relation  to  the 
fats  but  apparently  bearing  significant  biological  relationships, 
while  still  others  (like  certain  of  the  essential  oils)  appear  to 
bear  little  relationship  to  the  fats  and  to  be  classified  as  lipins 
merely  because  of  their  physical  properties.  If  the  term  "  lipins  " 
is  to  be  so  broadly  used,  it  may  be  convenient  to  apply  the 
term  "  lipoid  "  to  substances  other  than  fats  or  fatty  acids  but 
which  are  related  to  them  chemically  or  biologically. 

Prominent  among  the  Hpoids  (or  fat-like  substances  other 
than  true  fats)  are  the  sterols  (sohd  alcohols)  and  the  phospho- 
lipins or  phosphatids.  The  latter  are  substances  which  contain 
a  substituted  phosphoric  acid  radicle  in  place  of  one  or  more  of 
the  fatty  acid  radicles  of  a  fat. 

Sterols  occur,  at  least  in  small  amounts,  in  all  natural  fatsb 
The  best-known  sterols  are  cholesterol  (C27H44O)  and  phytosterol 
(C27H46O).  Cholesterol  occurs  in  animal  fats,  and  phytosterol 
(or  the  closely  related  sitosterol)  in  those  of  vegetable  origin. 
One  method  of  determining  whether  vegetable  fat  is  present  in 
butter  or  lard  is  to  examine  for  the  presence  of  phytosterol, 
since  phytosterol  is  not,  Hke  the  substances  to  which  the  color 
reactions  of  cottonseed  and  sesame  oils  are  due^  carried  over 
from  the  fat  of  the  food  to  that  of  the  animal  body. 

Although  its  functions  are  not  yet  clearly  defined,  cholesterol 
appears  to  be  a  substance  of  much  physiological  significance. 
The  name  indicates  "  bile-solid-alcohol,"  as  it  was  earliest  and 
best  known  as  a  prominent  constituent  of  gall  stones,  /its 
deposition  in  the  form  of  gall  stones  is  attributed  to  the  presence 


38  CHEMISTRY  OF  FOOD  AND  NUTRITION 

of  an  insufficient  amount  of  bile  salts  to  keep  the  cholesterol  of 
the  bile  in  solution.  It  may  also  be  deposited  in  the  walls  of 
the  arteries.  As  a  constituent  of  the  blood  cholesterol  acts  to 
protect  the  red  blood  cells  against  the  action  of  hemolytic  sub- 
stances, which  unless  neutrahzed  by  cholesterol  would  tend  to 
cause  anemia  through  excessive  destruction  of  red  corpuscles.\ 
According  to  Mathews,,  cholesterol  is  one  of  the  most  abundant 
lipins  of  the  brain  and  occurs  in  nearly  all  living  tissues ;  as  a 
constituent  of  waxes  and  the  sebum  of  the  skin  it  protects  the 
dermal  structures ;  it,  or  its  degradation  products,  aids  the  other 
lipins  in  giving  to  cells  their  power  of  holding  large  quantities 
of  water  without  dissolving  or  losing  their  peculiar  semifluid 
characters;  it  is  believed  to  bs  the  mother  substance  from 
which  the  i)ile  acids  are  derived  and  so  plays  an  important  part 
in  the  intestinal  digestion  and  absorption  of  fat;  and,  on  the 
other  hand,  cholesterol  itself  appears  to  check  the  action  of  fat- 
splitting  enzymes  in  the  body  and  thus  to  function  as  a  regu- 
lator in  the  metabolism  of  the  cell  lipins. 

Phospholipins  or  phosphatids  are  also  widely  distributed  in  liv- 
ing cells  and  doubtless  essential  to  their  structure  and  functions. 

Of  the  phospholipins  or  phosphatids  the  best-known  are  the 
lecithins,  which  are  abundant  in  egg  yolk  and  occur  also  in 
significant  quantities  in  brain  and  nerve  tissue,  blood,  lymph, 
milk,  many  seeds,  and  other  plant  and  animal  tissues.  ^The 
structure  of  lecithin  has  usually  been  represented  by  the  formula 
H 

I 
HC— OR 

I 
HC— OR 

I 
HC— O— PO(OH)— O— C2H4— N(CH3)0H. 

I 
H 

in  which  R  stands  for  a  fatty  acid  radicle. 


FATS  AND  LIPOIDS  39 

On  hydrolysis  such  a  compound  would  yield  glycerol,  fatty 
acids,  phosphoric  acid,  and  the  nitrogenous  base  choline  (tri- 
methyl  oxyethyl  ammonium  hydroxide).  If  one  of  the  radicles 
be  that  of  oleic  and  the  other  that  of  palmitic  acid  the  hydrolysis 
may  be  represented  thus: 

C42H84NPO9  +  4  H20-^  CsHgOs  +  C18H34O2  +  C16H32O2 

Glycerol  Oleic  Palmitic 

acid  acid 

+  H3PO4    +  C5H15NO2 

i  Phosphor-  ChoUne 

ic  acid 
Recent  investigations  throw  doubt  upon  the  view  that  the 
nitrogen  of  typical  lecithin  is  present  only  as  choline  groups. 

Taylor  defines  the  simpler  phosphatids  as  "  lipoids  in  which 
two  molecules  of  a  higher  fatty  acid  are  combined  with  glycerol- 
phosphoric  acid,  to  which  is  bound  an  amino  body." 

A  phosphatid  which,  like  the  above,  contains  one  atom  of 
nitrogen  and  one  of  phosphorus  to  the  molecule  is  classified  as 
a  monamino-monophospholipin  or  monamino-monophosphatid. 
Monamino-diphospholipins,  diamino-monophospholipins  and 
triamino-monophospholipins  have  also  been  described. 

The  fat  of  the  active  tissues  of  the  body,  as  distinguished 
from  that  of  the  adipose  tissue,  seems  to  consist  largely  of 
phospholipins. )  Thus  MacLean  and  WilHams  found  84  per  cent 
of  the  total  ether  extract  of  pigs'  liver  to  consist  of  phospholipins. 

Bang  holds  that  it  is  "  no  mere  coincidence  that  the  most 
highly  organized  cells  are  always  richest  in  lipoids." 

Other  lipoids  may  also  prove  to  be  of  much  importance  in 
nutrition.  Butter  fat  and  some  other  natural  fats  show  nutri- 
tive functions  which  cannot  be  attributed  to  their  glycerides 
alone  and  appear  to  be  due  to  other  substances  soluble  in  fats 
and  perhaps  of  the  nature  of  lipoids.  Such  as  yet  unidentified 
fat-soluble  substance  appears  to  be  absolutely  essential  to  a 
fully  complete  diet  since  several  investigators  (Stepp,  McCollum 
and  Davis,  Osborne  and  Mendel)  have  found  it  impossible  to 


40  CHEMISTRY  OF  FOOD  AND  NUTRITION 

raise  young  animals  to  full  maturity  on  rations  apparently  ade- 
quate otherwise  but  lacking  in  this  "  lipoid  "  of  "  fat-soluble  " 
factor.  These  experiments  will  be  cited  more  fully  in  con- 
nection with  the  discussion  of  the  specific  relations  of  food  to 
growth  (Chapter  XIII). 

REFERENCES 

Abderhalden.    Lehrbuch  der  Physiologische  Chemie. 

Abderhalden.     Biochemisches  Handlexicon. 

Abderhalden.    Handbuch  der  Biochemischen  Arbeitsmethoden. 

Bang.     Chemie  und  Biochemie  der  Lipoide. 

Bloor.  Absorption  and  Metabolism  of  Fat.  Journal  of  Biological  Chem- 
istry, Vol.  II,  page  429;  Vol.  15,  page  105;  Vol.  16,  page  517;  Vol.  17, 
page  377;  Vol.  19,  page  i;  Vol.  22,  page  133;  Vol.  23,  page  317; 
Vol.  24,  pages  227,   447  (1912-16). 

Browne.  The  Chemistry  of  Butter  Fat.  Journal  of  the  American  Chemical 
Society,  Vol.  21,  pages  632,  823,  975  (1899). 

GiES  AND  RosENBLOOM.  Classification  of  the  Lipins.  Biochemical  Bulletin, 
Vol.  I,  page  51  (191 2). 

Glikin.     Chemie  der  Fette,  Lipoide  und  Wachsarten. 

Hammarsten.     Textbook  of  Physiological  Chemistry. 

Hartley.  On  the  Fat  of  the  Liver,  Kidney  and  Heart.  Journal  of  Physi- 
ology, Vol.  38,  page  353  (1909). 

Henriques  AND  HANSEN.  Influence  of  Food  Fat  and  Other  Conditions 
upon  Body  Fat.  Skandinavisches  Archiv  Physiologie,  Vol.  11,  page  151 
(1901). 

Jordan  and  Jenter.  The  Source  of  Milk  Fat.  New  York  Agricultural 
Experiment  Station  (Geneva,  N.  Y.).  Bull.  132  (1897). 

Leathes.    The  Fats. 

Lewkowitsch.     Oils,  Fats  and  Waxes. 

MacLean  and  Williams.  Nature  of  the  Fat  of  the  Tissues  and  Organs. 
Biochemical  Journal,  Vol.  4,  page  455  (1909). 

McClendon.  Formation  of  Fats  from  Proteins  in  Eggs  of  Fish  and  Am- 
phibians.    Journal  of  Biological  Chemistry,  Vol.  21,  page  269  (1915)- 

Mathews.     Physiological   Chemistry. 

Mendel  and  Daniels.  Behavior  of  Fat-Soluble  Dyes  and  Stained  Fat 
in  the  Animal  Organism.  Journal  of  Biological  Chemistry,  Vol.  13, 
page  71  (1913)- 

Moulton  and  Trowbridge.     Composition  of  the  Fat  of  Beef  Animals 


FAT^ND  LIPOIDS  41 


M^^N 


on  Different  Planes  of  Nutrition.    Journal  of  Industrial  and  Engineering 

Chemistry,  Vol.  i,  page  761  (1909). 
Richardson.    Influence  of  Food  and  other  Conditions  on  the  Chemical 

Characteri^il^  of  Lard.    Journal  of  the  American  Chemical  Society, 

Vol.  26, "^^r 7,^2  (1904). 
Smedley.     Formation  of  Fat  from  Carbohydrate.    Biochemical  Journal, 

Vol.  7,  page  364  (1913)- 
Taylor.     Digestion  and  Metabolism. 
Ulzer  and  Klimont.    AUgemeine  und  Physiologische  Chemie  der  Fette. 


CHAPTER  III 

PROTEINS 

(  Carbohydrates  and  fats  are  the  chief  sources  of  energy  for 
the  activities  of  the  body,  but  not  the  chief  constituents  of  which 
the  active  tissues  are  composed.  Muscle  tissue,  for  instance, 
is  almost  devoid  of  carbohydrate  and  often  contains  very  httle 
fat.  The  chief  organic  constituents  of  the  muscles,  and  of  the 
protoplasm  of  plant  and  animal  cells  generally,  are  substances 
which  contain  nitrogen  and  sulphur  in  addition  to  carbon,  hy- 
drogen, and  oxygen.  Mulder,  in  1838,  des.cribed  a  nitrogenous 
material  which  he  believed  to  be  the  fundamental  constituent 
of  tissue  substances  and  gave  it  the  name  protein y  derived  from 
a  Greek  verb  meaning  "  to  take  the  first  plp,ce."  While  Mul- 
der's chemical  work  did  not  prove  to  be  of  permanent  value,  the 
term  which  he  introduced  has  been  retained,  and  in  the  plural 
form,  proteins,  is  now  used  as  a  group  name  t©  cover  a  large 
number  of  different  but  related  nitrogenous  organic  compounds 
which  are  so  prominent  among  the  constituents  of  the  tissues 
and  of  food  that  they  may  still  be  accorded  some  degree  of  pre- 
eminence in  a  study  of  the  chemistry  of  food  and  nutrition. 

Proteins  are  essential  constituents  of  both  plant  and  animal 
cells.  There  is  no  known  life  without  them.  Plants  build 
their  own  proteins  from  inorganic  materials  obtained  from  the 
soil  and  air.  Animals  form  the  proteins  characteristic  of  their 
own  tissues,  but  in  general  they  cannot  build  them  up  from  simple 
inorganic  substances  such  as  suffice  for  the  plants,  and  must 
depend  upon  the  digestion  products  obtained  from  the  proteins 
of  their  food.  Since  animals  must  have  proteins  for  the  con- 
struction and  repair  or  maintenance  of  their  tissues,  and  since, 

42 


PROTEINS  ,        43 

broadly  speaking,  they  cannot  make  their  proteins  except  from 
the  cleavage  products  of  other  proteins,  it  follows  that  proteins 
are  necessary  ingredients  of  the  food  of  all  animals. 

Chemical  Nature  and  Physical  Properties  of  Proteins  in  General 

Generally  speaking^,  the  proteins  of  different  kinds  of  tissue, 
and  even  of  the  corresponding  tissues  of  different  species,  are 
not  identical  substances.  The  total  number  of  different  proteins 
occurring  in  nature  must  therefore  be  very  great.  Of  these, 
some  fifty  or  sixty  have  been  sufficiently  isolated  and  studied 
to  warrant  description  as  chemical  individuals.  All  of  these 
have  proven  to  be  very  complex  substances  and  in  no  case  has 
the  chemical  structure  of  a  natural  protein  been  fully  deter- 
mined. It  has,  however,  been  shown  that  the  typical  protein^ 
are  essentially  anhydrides  of  the  following  amino  acids : 

AMINO  ACIDS  OF   COMMON  PROTEINS 

Mon^niino^onocarboxylitt'  acids 

Glycine,  amino-acetic  acid,  CH2(NH2)  •  COOH. 
Alanine,  a-amino-prof)ionic  acid,  CH3CH(NH2)  •  COOH. 
Vahne,  a-amino-isovaleric  acid,  (CH3)2CH  •  CH(NH2)  •  COOH. 
Leucine,    a-amino-isocaproic    acid     (a-amino-isobutyl-acetic 
acid), 

(CH3)2CH  •  CH2  •  CH(NH2)  •  COOH. 
Phenylalanine,  phenyl-a-amino-propionic  acid, 

C6H5CH2  •  CH(NH2)  •  COOH. 
Tyrosine,  oxyphenyl  a-amino  propionic  acid, 

C6H4(OH)  •  CH2  •  CH(NH2)  •  COOH. 
Serine,  a-amino-yS-hydroxy-propionic  acid, 

CH2(0H) :  CH(NH2)  •  COOH. 
Cystine  (dicysteine),  or  di-(a-amino-/8-thio-lactic  acid), 

S  -  CH2  -  CH(NH2)  •  COOH. 

S-CH2-CH(NH2)  •  COOH. 


44  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Monaminodicarboxylic  acids 
Aspartic  acid,  amino-succinic  acid, 

COOH  •  CH2  •  CH(NH2)  •  COOH. 
Glutamic  (glutaminic)  acid,  amino-glutaric  acid, 
COOH  •  CH2  •  CH2  •  CH(NH2)  •  COOH. 
Diaminomonocarboxylic  acids 
Ornithine,  a,  8,  diamino-valeric  acid, 

CH2(NH2)  •  CH2  •  CH2  •  CH(NH2)  •  COOH. 
Arginine,  8-guanidino-o-amino- valeric  acid, 
NH       . 
(H2N)C-  NHl-  CH2  •  CH2  •  CH2  •  CH(NH2)  •  COOH. 
Lysine,  a,  e,  diamino-]\-caproic  acid, 

CH2(NH2)  •  CH2    CH2  •  CH2  •  CH(NH2)  •  COOH. 
Heterocyclic  Amino  Acids : 
Histidine,  a-amino-/3-imidazol  propionic  acid, 
HC=C  •  CH2  •  CH(NH2)  •  COOH. 

I       I 
HN    N 

CH 

Proline,  pyrrolidin-carboxylic  acid, 
H2C — CH2 

I       I 
H2C     CH  •  COOH 

\/ 
NH 

Tryptophane,  a-amino-j8-indol-propionic  acid, 

CH 
HC^      \c C  •  CH2  •  CH  •  (NH2)  •  COOH. 

II 
CH 

^ch/  \nh 


PROTEINS 


45 


It  will  be  noted  that  these  constituents  of  the  protein  molecule 
differ  much  in  structure  among  themselves.  They  are,  how- 
ever, all  a-amino  acids,  i.e.,  the  amino  group  (or  one  of  them  if 
there  be  more  than  one)  is  attached  to  the  carbon  atom  adjacent 
to  the  carboxyl. 

In  view  of  the  wide  occurrence  of  the  alanine  radicle  in  proteins  and  the 
frequency  with  which  we  shall  have  occasion  to  discuss  the  behavior  of 
alanine  (as  a  typical  amino  acid)  in  metabolism,  it  may  be  of  interest  to 
point  out  that  several  of  the  amino  acids,  even  including  some  of  unique 
constitution,  may  be  regarded  as  derived  from  alanine  by  the  substitution 
of  a  simple  or  complex  radicle  for  one  of  the  hydrogens  on  the  /3  carbon  of 
alanine.  Thus  by  the  substitution  of  an  — OH  or  — SH  group  one  obtains 
serine  or  cysteine  respectively ;  by  substituting  the  phenyl  or  oxyphenyl 
group,  there  results  phenylalanine  or  tyrosine ;  by  the  imidazole  (C3H3N2), 
histidine ;  by  the  indol  (CsHeN)  radicle,  tryptophane. 


CH3 

I 
CHNH2 

I 
COOH 

Alanine 


CH2OH 


CHNHj 

I 
COOH 

Serine 


CHgCeHs 

I 
CHNH2 

I 
COOH 

Phenylalanine 


CHaCcHfiOH 

I 
CHNH2 

I 
COOH 

Tyrosine 


CH2C3H3N2 


CHNH2 


I 
COOH 

Histidine 


CH2SH 

I 
CHNH2 

I 
COOH 

Cysteine 

CH2C8H6N 

I 
CHNH2 

COOH 

Tryptophane 


The  linkage  of  the  amino  acid  radicles  in  the  protein  molecule  is 
chiefly  through  the  carboxyl  group  of  one  amino  acid  reacting 
with  the  amino  group  of  another..  Thus  two  molecules  of 
glycine  combined  by  ehmination  of  one  molecule  of  water 
yield  glycyl-glycine, 

CH2NH2-CO 


CH2NH-COOH. 

which  is  the  simplest  of  an  immense  group  of  anhydrides  of 
amino  acids,  all  of  which  are  called  "  peptids."    Dipeptids 


46  CHEMISTRY  OF  FOOD  AND  NUTRITION 

contain  two  amino  acid  radicles,  tripeptids  contain  three, 
etc.  Fischer,  by  uniting  7  to  19  amino-acid  radicles,  has  pro- 
duced synthetic  polypeptids  which  in  some  of  their  properties 
resemble  the  peptones,  the  simplest  substances  usually  regarded 
as  true  proteins.  Peptones  are  formed  in  nature  by  the  diges- 
tive hydrolysis  of  ordinary  proteins,  whose  structure  is  doubt- 
less considerably  more  complex. 

A  certain  analogy  between  carbohydrates  and  proteins  may 
be  noted.  As  starch  on  hydrolysis  yields  the  polysaccharide 
dextrins,  the  disaccharide  maltose,  and  finally  as  end  product 
the  monosaccharide  glucose,  so  the  native  protein  is  hydrolyzed 
through  peptones,  polypeptids,  and  di-  or  tri-peptids,  to  amino 
acids.  Thus  the  amino  acid  bears  the  same  general  relation  to 
the  protein  which  glucose  bears  to  starch ;  and  just  as  the  molec- 
ular weight  of  starch  is  very  high  and  a  single  starch  molecule 
yields  a  large  (unknown)  number  of  monosaccharide  molecules, 
so  the  molecular  weight  of  the  protein  is  very  high  and  the  pro- 
tein molecule  yields  a  large  (unknown)  number  of  amino  acid 
molecules.  There  is,  however,  this  important  difference :  the 
molecules  of  monosaccharide  resulting  from  complete  hydroly- 
sis of  starch  are  all  alike  (glucose),  whereas  the  complete  hy- 
drolysis of  any  typical  protein  yields  several  of  the  above-men- 
tioned amino  acids,  in  the  case  of  most  proteins  from  twelve  to 
twenty. 

In  view  of  the  marked  differences  in  structure  existing  among 
these  amino  acids  it  becomes  important  to  know  the  relative 
proportions  in  which  the  various  amino  acid  radicles  exist  in 
the  different  proteins.  This  is  studied  by  hydrolyzing  the  pro- 
tein and  separating  and  recovering  as  completely  as  possible  the 
amino  acids  resulting  from  the  hydrolysis.  Since  the  recovery 
of  the  amino  acids  cannot  be  accomplished  without  loss,  the 
results  obtained  are  not  strictly  quantitative  and  our  knowledge 
of  the  radicles  which  make  up  the  protein  molecule  remains 
incomplete.    It  is  beUeved  by  the  investigators  who  have  given 


PROTEINS 


47 


most  attention  to  the  question  that  the  failure  of  the  recovered 
amino  acids  to  show  a  summation  of  one  hundred  per  cent  is 
more  probably  due  to  unavoidable  losses  in  estimating  the  known 
amino  acids  than  to  the  presence  of  other  amino  acids  not  yet 
identified.  The  accompanying  table  shows  the  percentages  of 
amino  acids  obtained  from  four  proteins  occurring  in  different 
food  materials. 

Percentages  of  Amino  Acids  from  Four  Different  Pr*oteins  * 


Casein 
(from  Milk; 

Gelatin 

Gliadin 

(from 

Wheat) 

Zein 
(from  Maize) 

Glycine 

o.oo 

16.5 

0.00 

0.00 

Alanine    .     , 

1.50 

0.6 

2.00 

13.39 

Valine      .     . 

7.20 

I. 

3-34 

1.88 

Leucine   .     . 

9-35 

9.2 

6.62 

19.55 

Proline    .     . 

6.70 

10.4 

13-22 

9.04 

Aspartic  acid 

1-39 

1.2 

0.58 

1. 71 

Glutamic  acid 

15.5s 

16.8 

43.66 

26.17 

Phenylalanine 

3.20 

I. 

2.35 

6.55 

Tyrosine.     . 

4.50 

0. 

1.50 

3.55 

Serine      .     . 

.50 

•4 

.13 

1.02 

Oxyproline  . 

•23 

3-0 

— 

Histidine 

2.50 

•4 

1.84 

.82 

Arginine 

3.81 

9-3 

3.16 

1.55 

Lysine     .     . 

7.61 

6. 

0.92 

0.00 

Tryptophane 

1.5 

0.0 

I.O 

0.00 

Cystine    .     . 

.06 

— 

•45 

— 

Ammonia     . 

1.61 

•4 

5.22 

3.64 

Summation  . 

67.21 

76.21 

85.67 

88.87 

From  the  data  given  in  the  table  it  will  be  seen  that  the  pro- 
portions in  which  a  given  amino  acid  radicle  occurs  in  various 

*  In  general  each  figure  given  in  the  table  is  the  highest  of  the  resuhs  reported 
In  recent  investigations.  This  is  deemed  more  accurate  than  to  give  average  results, 
because  of  the  unavoidable  losses  referred  to  above. 

The  data  given  for  casein,  gUadin,  and  zein  are  taken  chiefly  from  the  work  of 
Osborne  and  his  associates;  those  for  gelatin  chiefly  from  that  of  Skraup  and 
Behler. 


48  CHEMISTRY  OF  FOOD  AND  NUTRITION 

proteins  may  be  quite  different.  The  four  proteins  here  shown 
yield  from  o.o  to  16.5  per  cent  of  glycine;  from  0.6  to  9.8  per 
cent  of  alanine;  from  i.o  to  7.2  per  cent  of  valine,  from  6.6  to 
19.6  per  cent  of  leucine.  Of  lysine,  zein  yields  none,  gliadin  about 
I  per  cent,  gelatin  6  per  cent,  and  casein  about  8  per  cent.  Of 
tryptophane,  zein  and  gelatin  yield  none,  gliadin  about  i  per 
cent,  casein  about  1.5  per  cent. 

For  more  detailed  comparisons  of  the  percentages  of  amino 
acids  in  different  proteins  and  also  in  the  flesh  of  four  widely 
separated  species,  the  more  extended  table  further  on  in  this 
chapter  may  be  consulted.  Whether  it  be  essential  that  the 
proteins  of  the  food  shall  furnish  all  the  amino  acids  which  the 
body  proteins  contain  will  naturally  depend  upon  whether  the 
body  is  able  to  make  individual  amino  acids  or  not.  Experi- 
mental evidence  has  shown  that  the  aninial  body  can  make 
glycine  readily,  so  that  the  absence  of  glycine  radicles  in  the  food 
proteins  does  not  detract  from  their  nutritive  value.  On  the 
other  hand  the  animal  body  does  not  seem  able  to  make  tryp- 
tophane, and  as  this  is  an  essential  constituent  of  body  tissue 
the  food  protein  must  always  furnish  tryptophane  if  it  is  to  meet 
the  needs  of  animal  nutrition.  Feeding  experiments  have  also 
shown  that  the  rate  of  growth  of  young  animals  may  be  largely 
influenced  by  the  lysine  content  of  the  proteins  fed ;  food  pro- 
teins in  which  lysine  is  lacking  or  inadequate  may  suffice  for  the 
maintenance  of  full  grown  animals  but  fail  to  support  normal 
growth  in  the  young  of  the  same  species. 

Such  facts  as  these  make  it  important  that  we  study  the 
proteins  not  only  as  a  group  but  also  individually  and  that  we 
learn  as  much  as  possible  about  the  kinds  and  amounts  of 
amino  acid  radicles  in  the  individual  proteins. 

The  ultimate  composition  of  the  proteins  shows  a  general 
similarity  throughout  the  group.  All  contain  carbon,  hydro- 
gen, oxygen,  nitrogen,  and  sulphur;  some  also  phosphorus 
or  iron. 


PROTEINS 


49 


Composition  of  Some  Typical  Proteins  according  to  Osborne 


Carbon 

Hydro- 
gen 

Nitro- 
gen 

Oxygen 

Sulphur 

Iron 

Phos- 
phorus 

CENT 

PER 
CENT 

PER 

CENT 

PER  CENT 

PER  CENT 

CENT 

PER 
CENT 

Egg-albumin     . 

52.7s 

7.10 

15.51 

23.024 

I.616 

Lact-albumin    . 

52.19 

7.18 

15-77 

23.13 

1.73 

Leucosin  .     .     . 

53.02 

6.84 

16.80 

22.06 

1.28 

Serum-globulin 

52.71 

7.01 

15.85 

23.32 

I. II 

Myosin    .     .     . 

52.82 

7.II 

16.67 

22.03 

1.27 

Edestin    .     .     . 

51.50 

7.02 

18.69 

21.91 

0.88 

Legumin  .     .     . 

51.72 

6.95 

18.04 

22.905 

0.385 

Casein      ,     .     . 

53.13 

7.06 

15.78 

22.37 

0.80 



oM^ 

Ovo-vitellin  .     . 

51.56 

7.12 

16.23 

23.242 

1.028 



^M 

Gliadin    .     .     . 

52.72 

6.86 

17.66 

21.733 

1.027 

Zein     .... 

55-23 

7.26 

16.13 

20.78 

0.60 

Oxyhemoglobin 

54.64 

7.09 

17.38 

20.165 

0.39 

0.335 

— 

It  will  be  seen  that  all  these  typical  proteins  contain  51  to 
55  per  cent  carbon,  about  7  per  cent  hydrogen,  20  to  23  per  cent 
oxygen,  15.5  to  18.7  per  cent  nitrogen,  0.3  to  2.0  per  cent  sulphur. 
Other  typical  proteins  thus  far  studied  have  shown  ultimate 
composition  within  these  same  limits. 

Similarity  of  elementary  composition  is  entirely  consistent  with  the 
belief  that  there  may  be  an  enormous  number  of  chemical  individuals  among 
the  proteins  of  nature. 

Fischer  has  recently  illustrated  the  vast  number  of  isomers  which  may 
exist  among  polypeptids  and  proteins  by  pointing  out  that  a  synthetic 
19-peptid  obtained  by  linking  15  glycine  and  4  leucine  molecules  is  only 
one  of  3876  possible  isomers,  without  considering  the  tautomerism  of  the  pep- 
tid  hnking.  When  more  than  two  kinds  of  amino  acids  are  involved,  the 
possible  number  of  isomers  increases  very  rapidly.  If  a  protein  be  imagined 
made  up  of  30  molecules  of  18  different  amino  acids,  one  taken  twice,  one 
3  times,  another  3,  one  4,  one  5  times,  and  13  taken  once  each,  there  would 
be  10  27  isomers  even  if  there  were  no  tautomerism  of  the  peptid  group  and 
if  the  linking  took  place  only  in  the  simple  way  as  with  monamino-mono- 
carboxylic  acids. 

It  is  easy  to  see  that  when  one  considers  not  only  isomerism  but  the  vast 
number  of  compounds  of  slightly  different  composition  which  can  be  obtained 


50  CHEMISTRY  OF  FOOD  AND   NUTRITION 

by  varying  the  kinds  and  proportions  of  the  amino  acid  radicals  in  the 
protein  molecule,  the  possible  number  of  different  proteins  of  very  similar 
elementary  composition  is  practically  unHmited. 

Probable  molecular  weights.  —  From  the  results  of  ultimate 
analysis  an  approximate  indication  of  the  minimum  molecular 
weight  may  often  be  obtained  by  a  very  simple  calculation. 
Thus,  oxyhemoglobin  contains  only  0.335  P^r  cent  of  iron,  and 
since  there  must  be  at  least  one  iron  atom  in  the  molecule,  it  is 
obvious  from  a  simple  proportion  making  use  of  the  atomic 
weight  of  iron, 

0.335:  56::  100  :rjc, 

that  the  molecular  weight  of  hemoglobin  must  be  in  the  neigh- 
borhood of  16,800  or  a  multiple  of  this. 

To  take  an  example  from  the  simple  proteins,  zein  contains 
0.60  per  cent  of  sulphur,  of  which  one  third  is  much  more  readily 
split  off  than  the  other  two  thirds,  from  which  it  appears  that 
the  molecule  contains  three,  or  a  multiple  of  three,  sulphur 
atoms.     Then  by  the  proportion, 

0.60:  (32  X  3)  -  100:0;, 

it  is  found  that  about  16,000  or  a  multiple  thereof  is  the  probable 
molecular  weight  of  zein. 

Estimates  of  the  same  order  of  magnitude  are  obtained  if  we 
base  our  calculations  on  the  proximate  rather  than  the  ulti- 
mate analyses  of  the  purified  protein  preparations.  Osborne, 
Van  Slyke,  Leavenworth,  and  Vinograd  have  recently  concluded 
from  a  very  searching  investigation  that  the  lysine  content  of 
gliadin  must  He  between  0.64  and  1.20  per  cent.  Since  the 
molecular  weight  of  lysine  is  146  it  follows  that  the  correspond- 
ing minimum  estimate  of  the  molecular  weight  of  ghadin  must 
fall  between  12,000  and  23,000.  The  experimental  facts  do 
not  permit  the  assumption  of  any  lower  molecular  weight  but 
are  not  inconsistent  with  the  view  that  the  true  molecular  weight 
may  be  some  multiple  of  this. 


PROTEINS  51 

Physical  properties.  —  In  only  a  few  cases  have  proteins 
been  obtained  in  crystalline  form.  Generally  speaking  the 
j)roteins  may  be  regarded  as  typically  colloidal  substances.  This 
does  not  preclude  the  behef  that  in  the  tissues  and  fluids  of  the 
body  the  proteins  may  exist  largely  in  combination  with  elec- 
trolytes. In  view  of  the  fact  that  the  behavior  of  proteins  in 
the  tissues  is  largely  dependent  upon  their  colloidal  character 
it  is  of  interest  to  bear  in  mind  the  very  high  molecular  weights 
of  the  proteins  as  mentioned  in  the  last  paragraph.  Discus- 
sions of  colloids  commonly  emphasize  the  fact  that  the  smallest 
particles  demonstrable  under  the  ultramicroscope  must  still 
be  of  quite  a  different  order  of  magnitude  from  that  calculated 
for  ordinary  molecules.  /In  such  a  case  as  that  of  starch  or  a 
typical  protein,  however,  the  probable  molecular  weight  is  so 
enormous  as  to  make  it  a  debatable  question  whether  the  in- 
dividual molecules  may  not  constitute  colloidal  particles  when 
dispersed  in  water  (BayHss). 

The  proteins  are  insoluble  in  all  of  the  solvents  for  fats 
(etker,  acetone,  chloroform,  carbon  disulphid,  carbon  tetrachlo- 
rid,  benzene,  and  petroleum  distillate).  They  differ  in  their 
solubilities  in  water,  salt  solutions,  and  alcohol,.)and  these  dif- 
ferences play  a  considerable  part  in  the  present  schemes  of 
classification. 

Classification.  —  There  was  formerly  considerable  confusion 
in  the  classification  and  terminology  of  the  proteins  and  some 
differences  of  usage  will  still  be  met  in  the  Hterature.  At  pres- 
ent, however,  the  majority  of  writers  follow  the  recommenda- 
tions made  by  a  joint  committee  of  the  American  Physiological 
Society  and  the  American  Society  of  Biological  Chemists  in 
December,  1907.  The  full  text  of  these  recommendations  will 
be  found  in  the  appendix.  The  following  is  an  outline  of  the 
classification  thus  recommended ;  to  which  have  been  added 
examples  covering  most  of  the  food  proteins  thus  far  described 
as  chemical  individuals. 


52  CHEMISTRY  OF  FOOD  AND  NUTRITION 

t.  Simple  Proteins.  Protein  substances  which  yield  only 
amino  acids  or  their  derivatives  on  hydrolysis. 

(a)  A  Ibumins.  Simple  proteins  soluble  in  pure  water  and  coag- 
ulable  by  heat.  Examples :  egg  albumin,  lactalbumin  (milk), 
serum  albumin  (blood),  leucosin  (wheat),  legumelin  (peas). 

{b)  Globulins.  Simple  proteins  insoluble  in  pure  water,  but 
soluble  in  neutral  salt  solutions.  Examples:  muscle  globulin, 
serum  globulin  (blood),  edestin  (wheat,  hemp  seed,  and  other 
seeds),  phaseolin  (beans),  legumin  (beans  and  peas),  vignin 
(cow  peas),  tuberin  (potato),  amandin  (almonds),  excelski 
(Brazil  nuts),  arachin  and  conarachin  (peanuts). 

{c)  Glutelins.  Simple  proteins  insoluble  in  all  neutral  solvents, 
but  readily  soluble  in  very  dilute  acids  and  alkalies.  The  best- 
known  and  most  important  member  of  this  group  is  the  glu- 
tenin  of  wheat. 

{d)  Alcohol  soluble  proteins.  Simple  proteins  soluble  in 
relatively  strong  alcohol  (70-80  per  cent)  but  insoluble  in  water, 
absolute  alcohol,  and  other  neutral  solvents.  Examples :  glia- 
din  (wheat),  zein  (corn),  hordein  (barley),  kafirin  (kafir  corn). 

{e)  Albuminoids.  These  are  the  simple  proteins  character- 
istic of  the  skeletal  structures  of  animals  (for  which  reason  they 
are  also  called  scleroproteins)  and  also  of  the  external  pro- 
tective tissues,  such  as  the  skin,  hair,  etc.  None  of  these  pro- 
teins is  used  for  food  in  the  natural  state,  but  collagen  when 
boiled  with  water  yields  gelatin. 

(/)  Histones.  Soluble  in  water,  and  insoluble  in  very  dilute 
ammonia,  and  in  the  absence  of  ammonium  salts  insoluble 
even  in  an  excess  of  ammonia ;  yield  precipitates  with  solutions 
of  other  ptoteins  and  a  coagulum  on  heating  which  is  easily 
soluble  in  very  dilute  acids.  On  hydrolysis  they  yield  several 
amino  acids,  among  which  the  basic  ones  predominate.  The 
only  members  of  this  group  which  have  any  considerable  im- 
portance as  food  are  the  thymus  histone  and  the  globin  derived 
from  the  hemoglobin  of  the  blood. 


PROTEINS  53 

(g)  Protamins.  These  are  simpler  substances  than  the 
preceding  groups,  are  soluble  in  water,  not  coagulable  by  heat, 
possess  strong  basic  properties,  and  on  hydrolysis  yield  a  few 
amino  acids  among  which  the  basic  amino  acids  greatly  pre- 
dominate.    They  are  of  no  importance  as  food. 

U.  Conjugated  Proteins.  Substances  which  contain  the 
protein  molecule  united  to  some  other  molecule  or  molecules 
otherwise  than  as  a  salt. 

{a)  Nucleo proteins.  Compounds  of  one  or  more  protein 
molecules  with  nucleic  acid.  Examples  of  the  nucleic  acids 
thus  found  united  with  proteins  are  thy  mo-nucleic  acid  (thy- 
mus gland),  tritico-nucleic  acid  (wheat  germ). 

(b)  Glycoproteins.  Compounds  of  the  protein  molecule 
with  ^  substance  or  substances  containing  a  carbohydrate 
group  other  than  a  nucleic  acid.     Example :   mucins. 

(c)  Phosphoproteins.  Compounds. in  which  the  phosphorus 
is  in  organic  union  with  the  protein  molecule  otherwise  than 
in  a  nucleic  acid  or  lecithin,'  Examples:  caseinogen  (milk), 
ovovitelHn  (egg  yolk). 

.  {d)  Hemoglobins.  Compounds  of  the  protein  molecule  with' 
hematin  or  some  similar  substance.  Example :  hemoglobin  of 
blood.  (The  redness  of  meat  is  due  chiefly  to  the  hemoglobin 
of  the  blood  which  the  meat  still  retains.) 

{e)  Lecithoproteins.  Compounds  of  the  protein  molecule 
with  lecithins  or  related  substances. 

III.  Derived  Proteins. 

I.  Primary  protein  derivatives.  Derivatives  of  the  protein 
molecule  apparently  formed  through  hydrolytic  changes  which 
involve  only  shght  alterations. 

{a)  Proteans.  Insoluble  products  which  apparently  result 
from  the  incipient  action  of  water,  very  dilute  acids,  or  enzymes. 
Examples:  casein  (curdled  milk),  fibrin  (coagulated  blood). 

{b)  Metaproteins.  Products  of  the  further  action  of  acids 
and  alkalies  whereby  the  molecule  is  sufficiently  altered  to  form 


54  CHEMISTRY  OF  FOOD  AND  NUTRITION 

proteins  soluble  in  very  weak  acids  and  alkalies,  but  insoluble 
in  neutral  solvents.  This  group  includes  the  substances 
which  have  been  called  "  acid  proteins,"  "  acid  albumins," 
"  syntonin,"  "  alkali  proteins,"  "  alkali  albumins,"  and 
*'  albuminates." 

(c)  Coagulated  proteins.  Insoluble  products  which  result 
from  (i)  the  action  of  heat  on  protein  solutions,  or  (2)  the  action 
of  alcohol  on  the  protein.  Example :  cooked  egg  albumin,  or 
egg  albumin  precipitated  by  means  of  alcohol. 

2.  Secondary  protein  derivatives.  Products  of  the  further 
hydrolytic  cleavage  of  the  protein  molecule. 

(a)  Proteoses.  Soluble  in  water,  not  coagulable  by  heat, 
precipitated  by  saturating  their  solutions  with  ammonium 
sulphate  or  zinc  sulphate.  The  products  commercially  known 
as  "  peptones  "  consist  largely  of  proteoses. 

(b)  Peptones.  Soluble  in  water,  not  coagulable  by  heat,  and 
not  precipitated  by  saturating  their  solutions  with  ammonium 
sulphate  or  zinc  sulphate.  These  represent  a  further  stage  of 
cleavage  than  the  proteoses. 

(c)  Peptids.  Definitely  characterized  combinations  of  two 
or  more  amino  acids.  An  anhydride  of  two  amino  acid  radicles 
is  called  a  "  di-peptid  " ;  one  having  three  amino  acid  radicles, 
a  "  tri-peptid  " ;  etc.  Peptids  result  from  the  further  hydro- 
lytic cleavage  of  the  peptones.  As  was  mentioned  above,  many 
peptids  have  also  been  made  in  the  laboratory  by  the  Hnking 
together  of  amino  acids. 

Substances  simpler  than  the  peptones  but  containing  several 
amino  acid  radicles  are  often  called  "  polypeptids." 

Properties  of  Some  Individual  Proteins 

1 
Albumins  and  globulins  are  very  often  associated,  as,  for 

example,  in  blood  serum  and  in  the  cell  substance.     As  a  rule 

the  albumins  are  the  more  abundant  in  animal  fluids,  while 


PROTEINS  55 

the  globulins  predominate  over  albumins  in  animal  tissues  and 
in  plants.  iXhere  appears  to  be  no  sharp  dividing  line  between 
the  albumins  and  the  globuHns.  While  the  globuHns  are  in- 
soluble in  pure  water,  a  water  extract  of  animal  tissue  (muscle, 
for  example)  will  contain,  in  addition  to  albumin,  a  considerable 
amount  of  globulin  carried  into  solution  by  the  salts  present  in 
the  tissue,  and  if  the  salts  are  removed  as  completely  as  possible 
by  dialysis,  some  of  the  globulin  still  remains  in  solution ;  sepa- 
rations based  upon  saturation  with  neutral  salts  are  also  apt 
to  be  unsatisfactory^  (Howell). 

Notwithstanding  these  difficulties,  a  considerable  number  of 
individual  albumins  and  globuHns  have  been  isolated,  purified, 
and  analyzed.  In  ultimate  composition  they  show  a  general 
similarity  except  that  the  albumins  are  richer  in  sulphur  than 
the  globuHns. 

Several  members  of  each  group  have  also  been  studied  to 
determine  the  kinds  and  amounts  of  amino  acid  radicles  which 
they  contain,  with  the  results  shown  in  the  table  on  pages  60 
and  61.  It  is  of  interest  to  compare  the  amino  acid  make-up 
of  typical  proteins  with  their  adequacy  in  nutrition.  A  few 
studies  of  this  sort,  notably  those  of  Kauffmann  with  gelatin 
and  Willcock  and  Hopkins  with  zein,  had  been  made  some  years 
earHer,  but  much  the  greater  part  of  our  knowledge  in  this 
field  is  due  to  the  recent  investigations  of  Osborne  and  Mendel 
(191 1  et  seq.).  Rats  have  been  chiefly  used  as  the  experimental 
animal. 

Egg  albumin,  perhaps  the  most  familiar  of  all  proteins  and 
the  one  most  often  chosen  to  illustrate,  in  the  laboratory,  the 
properties  of  proteins  in  general,  will  be  seen  to  yield  no  glycine 
but  to  furnish  all  the  other  usual  amino  acids  in  quite  appreciable 
proportions.  The  feeding  experiments  show  that  with  a  diet 
adequate  as  regards  all  other  factors  animals  may  be  maintained 
in  normal  nutrition  and  young  animals  may  make  normal 
growth  with  egg  albumin  as  the  sole  protein  food. 


56  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Lactalbumin  shows  this  same  property  in  even  greater  degree. 
It  appears  to  be  the  most  efficient  in  supporting  growth  of  all 
the  proteins  which  have  been  studied,  and  this  is  beHeved  to 
be  due  primarily  to  its  high  lysine  content  (see  table  beyond). 

Legumelin  and  leucosin  have  not  yet  been  studied  in  feeding 
experiments  of  this  kind,  nor  have  such  experiments  been  made 
with  amandin  or  vicilin. 

Only  preliminary  feeding  experiments  not  entirely  success- 
ful as  regards  growth  have  been  reported  for  legumin,  phaseolin, 
and  vignin;  but  each  of  the  other  three  vegetable  globulins 
shown  —  edesHn,  excelsin,  and  glycinin  —  has  been  found  to 
suffice  for  maintenance  and  normal  growth  when  fed  as  the 
sole  protein  in  a  diet  adequate  in  other  respects.*  In  fact 
Osborne  and  Mendel  have  kept  one  family  of  rats  through  three 
generations  with  edestin  as  a  sole  protein  food. 

Glutelins  and  the  alcohol-soluble  proteins  (prolamins)  are  im- 
portant as  constituents  of  the  cereal  grains.  The  best-known 
examples  of  the  respective  groups  are  glutenin  and  gUadin  of 
wheat  flour.  These  proteins  resemble  each  other  in  ultimate 
composition,  but  differ  not  only  in  solubiHties,  but  also  in  their 
cleavage  products.  They  are  much  the  most  important  of  the 
proteins  of  the  wheat  kernel,  the  gHadin  making  up  about  50 
per  cent  and  the  glutenin  about  40  per  cent  of  the  total  protein 
present.  The  gliadin  and  glutenin  together  constitute  the  glu- 
ten of  wheat  flour. 

Glutenin  (wheat  glutehn)  and  maize  glutelin  have  each  been 
shown  capable,  in  the  rat-feeding  experiments  cited  above,  of 
meeting  the  requirements  not  only  of  maintenance  but  also  of 
normal  growth  when  fed  as  the  sole  protein  food  in  diets  adequate 
in  other  respects. 

Gliadin,  hordein,  and  the  prolamin  of  rye,  when  fed  singly  in 
the  same  manner,  are  found  capable  of  maintaining  grown  rats 

*  Factors  necessary  to  make  a  diet  adequate  will  be  discussed  in  Chapters  XII 
and  XIII,  where  experiments  upon  growth  will  be  considered  in  greater  detail. 


PROTEINS  57 

but  not  of  supporting  normal  growth.  .  Zein,  fed  alone  in  similar 
experiments,  did  not  suffice  either  for  maintenance  or  for  growth. 
Osborne  and  Mendel  concluded  from  these  experiments  that 
the  failure  even  to  maintain  the  grown  animals  was  due  to  the 
absence  of  tryptophane ;  while  the  failure  of  the  rats  to  grow 
on  gliadin,  hordein,  or  rye  prolamin  was  due  to  the  fact  that 
these  proteins  either  lack  lysine  or  contain  it  in  insufficient  quan- 
tity. This  interpretation  was  confirmed  by  later  experiments 
in  which  they  found  that  adding  tryptophane  to  the  zein  food 
made  it  adequate  for  maintenance  and  adding  lysine  to  the 
gliadin  food  made  it  adequate  to  support  growth. 

(gelatin,  the  only  member  of  the  albuminoids  (sderoproteins) 
which  is  of  practical  importance  as  food,  has  long  been  known  to 
be  unable  to  support  protein  metabolism  when  fed  as  the  sole 
protein  food.  This  inadequacy  now  appears  to  be  due  to  the 
absence  of  tryptophane  and  tyrosine  and  perhaps  in  part  also  to 
the  fact  that  some  of  the  other  amino  acids,  cystine  and  histidine, 
are  furnished  by  gelatin  in  only  very  small  proportion.  As 
early  as  1905  Kauffmann  tried  the  experiment  of  living  upon  a 
diet  in  which  gelatin  was  the  sole  protein,  but  was  supplemented 
by  additions  of  tyrosine,  tryptophane,  and  cystine.  So  far  as 
could  be  determined  by  a  short  experiment  the  addition  of  these 
amino  acids  seemed  to  make  good  the  deficiencies  of  the 
gelatin. 

Nucleoproteins  are  the  characteristic  proteins  of  cell  nuclei, 
and  are  therefore  especially  abundant  in  the  highly  nucleated 
cells  of  the  glandular  organs,  such  as  the  thymus,  the  pancreas, 
and  the  liver.  They  are  compounds  of  simple  proteins  with 
nucleic  acid  or  nuclein.  The  chemical  nature  of  the  latter  and 
their  behavior  in  metaboUsm  will  be  considered  in  Chapter  V. 

Phosphoproteins  occur  especially  in  milk  and  eggs,  which  ob- 
viously function  in  nature  to  provide  the  material  for  growth  and 
development  of  new  animal  tissue.  ;  The  phosphorus,  while  prob- 
ably present  in  the  form  of  a  more  or  less  modified  phosphoric 


58 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


acid  radicle,  appears  to  be  more  closely  bound  in  these  than  in 
the  nucleoproteins.  Casein  of  milk  and  the  vitellin  of  egg  yolk 
(ovo-vitellin)  are  the  most  prominent  members  of  the  group. 
These  are  sometimes  classed  with  simple  proteins  under  the 
name  nucleo-albumins.  Phosphoprotein  preparations  show  on 
analysis  small  amounts  of  iron,  which  has  usually  been  neglected 
as  an  impurity  but  which  is  not  improbably  an  essential  con- 
stituent. 

Casein  and  ovo-vitellin  fed  singly  as  the  sole  protein  of  the 
ration  in  the  experiments  by  Osborne  and  Mendel  described 


Curves  of  Growth  on  Foods  containing  a  Single  Protein  _ 


Fig.  I.  —  Showing  typical  curves  of  growth  of  rats  on  diets  otherwise  similar  and 
adequate  but  containing  in  each  case  only  a  single  protein,  casein,  gliadin,  or  zein. 
Courtesy  of  Dr.  L.  B.  Mendel  and  the  Journal  of  the  American  Medical  Association. 

above  have  each  been  found  capable  of  supporting  both  main- 
tenance and  normal  growth,  as  their  amino  acid  make-up  and 
their  place  in  nature  would  lead  us  to  expect.  The  curves  in 
Fig.  I  illustrate  the  rapid  growth  on  casein  as  compared  with 
the  very  slow  growth  on  gliadin  and  the  loss  of  weight  when 
zein  was  the  sole  protein  food.    The  rations  were  alike  except 


PROTEINS  59 

for  the  nature  of  the  protein  fed;  the  percentage  of  protein 
in  the  ration  was  the  same  in  each  case. 

It  will  be  seen  that  the  rat  receiving  casein  grew  over  200 
grams  in  140  days  while  the  one  fed  with  gliadin  grew  only  20 
grams  during  the  same  period.  The  third  rat,  which  had  been 
growing  rapidly  on  mixed  food,  began  at  once  to  lose  weight  when 
put  on  a  ration  of  which  zein  was  the  sole  protein. 

Hemoglobins,  consisting  of  combinations  of  simple  proteins 
with  coloring  matter,  serve  as  carriers  of  oxygen  from  the  air 
to  the  tissues.  On  boiling  or  heating  with  acids  or  alkalies  they 
are  split  into  their  constituent  parts:  for  example,  ordinary 
hemoglobin  yields  about  4  per  cent  of  hematin,  C32H32N4Fe04, 
and  a  residue  of  globin  which  was  formerly  considered  a  globulin 
but  is  now  assigned  to  the  histone  group. 

Proteoses  and  peptones  are  products  derived  from  other  pro- 
teins by  digestion  or  by  simple  hydrolysis.  They  are  soluble 
in  water  and  not  coagulated  by  boiUng  their  aqueous  solutions. 
No  sharp  line  can  be  drawn  either  between  proteoses  and  pep- 
tones, or  between  peptones  and  the  simpler  nitrogen  compounds 
which  result  from  prolonged  digestion.,  As  the  terms  are  gen- 
erally used,  peptones  may  be  considered  as  the  products  of  diges- 
tion or  hydrolysis  which  still  show  the  usual  color  reactions  of 
proteins  and  are  precipitated  by  strong  alcohol ;  but  are  not 
precipitated  by  saturation  of  their  solutions  with  zinc  or  ammo- 
nium sulphate,  as  is  the  case  with  proteoses.  Proteoses  (albu- 
moses)  are  intermediate  products  between  metaprotein  and  pep- 
tones. In  addition  to  the  protein  reactions  shown  by  peptones, 
the  proteoses  are  precipitated  from  aqueous  solutions  at  ordinary 
temperatures  by  adding  acetic  acid  and  potassium  ferrocyanide, 
or  by  saturating  the  solution  with  zinc  or  ammonium  sulphate. 

The  term  "  peptone  "  was  formerly  appHed  to  all  digestion 
products  not  coagulated  by  boiHng,  and  is  still  popularly  used 
in  the  same  sense,  the  best  commercial  "  peptones  "  consisting 
largely  of  proteoses. 


6o 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


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PROTEINS 


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62  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Relation  between  Chemical  Constitution  of  the  Proteins  and 
Their  Food  Value 

Several  facts  bearing  upon  the  relation  between  the  feeding 
values  of  individual  proteins  and  their  amino  acid  make-up  have 
been  cited  in  the  preceding  pages.  The  subject  is  of  great  im- 
portance and  is  now  under  active  investigation.  Since  the 
experimental  facts  are  still  being  determined,  any  attempt  to 
generalize  broadly  at  this  point  would  be  premature.  A  few 
important  conclusions  may,  however,  be  deduced  from  the  facts 
already  given. 

Glycine,  although  an  essential  constituent  of  body  tissue,  need 
not  be  furnished  by  the  food,  for  several  proteins  which  do  not 
yield  glycine  on  hydrolysis  have  been  shown  to  be  adequate  when 
fed  as  sole  protein  of  an  experimental  ration.  It  appears 
therefore  that  supphes  of  glycine  fully  adequate  to  meet  all 
normal  needs  may  be  formed  within  the  body  itself. 

Tryptophane,  on  the  other  hand,  apparently  must  always  be 
suppHed  to  the  animal  body;  food  furnishing  no  tryptophane 
has  always  proven  inadequate  even  for  maintenance  of  full- 
grown  animals.  Apparently  the  animal  body  is  unable  to  make 
tryptophane  (or  at  least  to  make  it  at  the  rate  required  for 
normal  metabolism)  and  proteins  lacking  the  tryptophane  radicle 
must  be  regarded  as  always  inadequate  as  a  sole  protein  food.  / 

Lysine,  again,  is  especially  important  in  connection  with 
growth.  Proteins  which  yield  Httle,  if  any,  lysine  (and  which 
are  otherwise  adequate  in  their  amino  acid  make-up)  appear 
to  suihce  as  the  sole  protein  food  in  the  maintenance  of  full- 
grown  animals  (rats)  but  not  to  support  a  normal  growth  of 
the  young. 

As  regards  the  influence  of  the  presence  or  absence  of  glycine, 
lysine,  and  tryptophane  radicles  in  the  protein  molecule,  it 
seems  possible  to  correlate  the  chemical  structure  and  the 
nutritive  value  of  the  proteins  quite  definitely.     In  establish- 


PROTEINS 


63 


ing  this  correlation,  Osborne  and  Mendel  have  made  one  of  the 
most  important  advances  in  the  entire  development  of  the 
chemistry  of  food  and  nutrition. 

That  the  inadequacy  of  zein  for  maintenance  is  essentially 
due  to  the  lack  of  tryptophane,  they  demonstrated  by  feeding  a 
ration  with  zein  as  sole  protein  but  with  tryptophane  added. 
This  mixture  permitted  maintenance  without  growth  (rat  1892, 
middle  portion  of  Fig.  2).  Then  by  the  addition  of  lysine  to 
the  zein  and  tryptophane  diet  they  induced  normal  growth  as 
shown  by  the  continuation  of  the  weight  curve  of  rat  1892  at 


Fig.  2.  —  Showing  the  effect  of  adding  tryptophane  or  tryptophane  and  lysine  to 
a  diet  containing  zein  as  the  sole  protein  (compare  Fig.  i,  page  58).  Courtesy  of 
Dr.  L.  B.  Mendel  and  the  Journal  of  the  American  Medical  Association. 

the  right  of  Fig.  2.  In  another  case  (rat  1773,  at  the  left  of 
Fig.  2)  a  rat  which  was  rapidly  losing  weight  on  the  zein  diet 
was  restored  to  a  condition  of  normal  growth  by  the  addition 
of  tryptophane  and  lysine  to  the  food. 

As  Mendel  expresses  it :  "  If  we  analyze  the  situation  as 
revealed  in  the  charts  of  some  actual  experiments,  it  becomes 
apparent  that  both  lysine  and  tryptophane  are  unquestionably 
necessary  as  constructive  units  in  growth.  The  dechne  brought 
about  by  the  zein  food  can  be  stopped  by  the  addition  of  trypto- 
phane, as  such,  to  the  diet.  This  results  in  maintenance ;  but 
no  growth  ensues  until  lysine  also  is  added." 

Osborne  and  Mendel  also  showed  that  the  addition  of  lysine 
to  the  gliadin  ration  made  it  adequate  to  support  normal 


64 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


growth.  They  have  also  shown  that  retardation  of  growth  may 
sometimes  be  due  to  restricted  intake  of  some  amino  acid  other 
than  lysine. 

In  the  experiments  above  described  the  rations  always  con- 
tained a  liberal  amount  (usually  i8  per  cent)  of  protein.  If, 
on  the  other  hand,  the  percentage  of  protein  in  the  food  be 


320 


280 


240 


200 


•S    /20 


4*. 


60  -' 


40 


/*_., 

C    -  J 

1 

/ 

/ 

•*___.•_  .  /*...^ 

k-     ^     •    •   r     - 

Case 

'in  T  ^i/si 

me  *  *•* 

\^ 

/ 

/ 

/ 

r 

I           1 
1 

' r 

/ 

( 

f 

J 

\  I 

1          1 

4 

<> 
^^^ 

Y 

\ 

V 

40  Days 

Fig.  3.  —  Showing  that  the  insufficiency  of  a  low-casein  diet  was  essentially  due 
to  its  relative  deficiency  in  cystine.  Courtesy  of  Dr.  L.  B.  Mendel  and  the  Journai 
of  the  American  Medical  Association. 


sufficiently  reduced,  the  growth  may  be  retarded  even  though  the 
protein  be  of  a  kind  which  is  entirely  adequate  when  liberally 
fed.  Thus  on  a  ration  containing  9  per  cent  of  casein  the  rats 
grew  only  about  half  as  rapidly  as  when  they  received  18  per 
cent ;  *  and  in  this  case  the  limiting  factor  was  not  lysine  but 

*  On  account  of  the  very  diflferent  rates  of  growth,  not  to  mention  other  differ- 
ences between  the  species,  one  must  not  attempt  to  apply  the  quantitive  data  of 
the  rat-feeding  experiments  directly  to  the  problem  of  protein  requirement  in  man. 


PROTEINS  65 

cystine,  for  the  addition  of  cystine  to  the  low-casein  diet  in- 
duced a  normal  rate  of  growth  which  was  immediately  checked 
when  the  cystine  was  withdrawn  and  resumed  when  the  cystine 
was  again  added  to  the  ration  (Fig.  3). 

In  all  of  the  experiments  cited  thus  far  each  ration  contained 
only  a  single  isolated  protein.  This  is  the  ideal  condition  for 
the  experimental  comparison  of  individual  proteins,  but  is  quite 
different  from  ordinary  or  "practical"  conditions,  since  our' 
common  protein  foods  all  contain  mixtures  of  proteins,  so  that 
even  if  only  a  single  article  of  food  were  consumed  the  diet 
would  still  furnish  more  than  one  protein  at  a  time.  By  feed- 
ing definite  mixtures  of  pure  proteins  Osborne  and  Mendel  have 
beautifully  demonstrated  the  way  in  which  proteins  supple- 
ment each  other  in  nutrition.  Thus  zein  alone  is,  as  we  have 
seen,  always  inadequate  as  a  sole  protein  food ;  lactalbumin  is 
adequate  when  fed  in  sufficient  quantity  but  when  constituting 
only  4.5  per  cent  of  the  food  mixture  of  rats  it  supports  only 
slow  growth;  but  a  food  mixture  containing  4.5  per  cent  of 
lactalbumin  and  13.5  per  cent  of  zein  supports  growth  at  a 
fully  normal  rate  (Fig.  4).  This  shows  that  a  relatively  small 
amount  of  lactalbumin  (one  fourth  of  the  protein  fed)  sufficed 
to  furnish  the  amino  acid  groups  which  the  zein  lacked.  It 
shows  also  that  zein,  which  when  fed  as  a  sole  protein  is  insuf- 
ficient even  for  maintenance,  is  able  as  a  constituent  of  a  proper 
food  mixture  to  take  part  in  supplying  the  materials  for  growth, 
to  such  an  extent  as  to  more  than  double  the  growth-rate.  Thus 
zein,  although  inadequate  for  either  maintenance  or  growth  when 
isolated  and  fed  alone,  may  nevertheless  take  an  important 
part  in  both  maintenance  and  growth  when  fed  as  a  part  of  a 
proper  mixed  diet.  Moreover  it  may  not  even  be  necessary  to 
resort  to  a  mixture  of  food  materials  in  order  to  make  good  the 
deficiencies  of  the  individual  incomplete  protein.  Corn  (maize) 
itself,  along  with  zein,  contains  an  almost  equal  amount  of 
another  protein,  maize  glutelin,  which  Osborne  and  Mendel 


66 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


have  shown  to  be  capable  of  supporting  a  normal  rate  of  growth 
—  not  to  mention  the  proteins  in  the  embryo  of  the  maize 
kernel  which  appear  to  have  a  still  higher  nutritive  efficiency 
(Hart  and  Humphrey;  McCollum  and  Davis). 

Thus  it  is  plain  that  the  mixtures  of  proteins  contained  in 
different  articles  of  food  as  we  eat  them  do  not  differ  in  such  a 


JZO 
280 
240 
200 

/ 

^ 

'X 

/ 

^ 

•5    120 

% 

40. 

f 

•Ji 

^ 

/ 

..^^ 

»5> 

/ 

40  Days 

Fig.  4.  —  Showing  the  efficiency  of  lactalbumin  as  a  supplement  to  zein,  and  also 
that  zein  may  take  an  important  part  in  growth  although  zein  alone  is  inadequate 
either  for  growth  or  maintenance.  Courtesy  of  Dr.  L.  B.  Mendel  and  the  Journal 
of  the  American  Medical  Association. 

Striking  way  as  do  the  individual  proteins  when  isolated  and 
fed  singly ;  but  neither  is  it  true  that  the  proteins  of  different 
articles  of  food  are  equivalent  for  all  practical  purposes.  Hart, 
McCollum,  and  their  associates  have  shown  that  the  natural 
protein  mixture  of  milk  is  more  efficient  than  an  equal  weight 
of  the  mixed  proteins  of  wheat  or  corn  (maize)  both  for  the  sup- 
port 01  growth  in  young  animals  (pigs)  and  as  food  for  the  pro- 


PROTEINS  67 

duction  of  milk  in  dairy  cattle.  While  it  is  always  possible  that 
in  comparisons  between  natural  food  materials  the  results  may 
be  influenced  by  differences  in  the  unknown  food  constituents 
which  may  be  present,  yet  in  the  cases  here  cited  it  is  probable 
that  the  differing  efficiencies  ascribed  to  milk  and  grain  proteins 
are  mainly  due  to  the  same  differences  of  chemical  constitution 
(''amino  acid  make-up")  to  which  are  attributable  the  striking 
results  obtained  in  the  experiments  previously  cited  in  which 
isolated  foodstuffs  were  fed. 

REFERENCES 

Abderhalden.     Lehrbuch  der  Physiologische  Chemie. 

Fischer.     Untersuchungen  iiber  Aminosauren,  Polypeptide  und  Proteine. 

Ceiling.  The  Nutritive  Value  of  the  Diamino-Acids  occurring  in  Proteins 
for  the  Maintenance  of  Adult  Mice.  Journal  of  Biological  Chemistry, 
Vol.  31,  page  173  (1917). 

Hart  and  Humphrey.  The  Relation  of  the  QuaKty  of  Proteins  to  Milk 
Production.  Journal  of  Biological  Chemistry,  Vol.  21,  page  239  (1915) ; 
Vol.  26,  page  457  (1916) ;  Vol.  31,  page  445  (1917). 

Hammarsten.     Textbook  of  Physiological  Chemistry. 

Hawk.     Practical  Physiological  Chemistry. 

Jones.  The  Nucleic  Acids ;  their  Chemical  Constitution  and  Physiological 
Conduct. 

KossEL.  Lectures  on  the  Herter  Foundation.  The  Proteins.  Bulletin 
of  the  Johns  Hopkins  Hospital,  Vol.  23,  page  65  (191 2). 

Mann.     Chemistry  of  the  Proteids. 

Mathews.     Physiological  Chemistry. 

McCoLLUM.  The  Value  of  Cereal  Proteins  for  Growth.  Journal  of  Bio- 
logical Chemistry,  Vol.  19,  page  323  (1914). 

McCoLLUM  AND  Davis.  Nutrition  with  Purified  Food  Substances.  Jour- 
nal of  Biological  Chemistry,  Vol.  20,  page  641  (1915) ;  The  Cause  of 
the  Loss  of  Nutritive  EflSciency  of  Heated  Milk,  Ihid.,  Vol.  23,  page 
247  (1915). 

Mendel.  Nutrition  and  Growth.  The  Harvey  Society  Lectures  for 
1914-1915,  page  loi;  and  Journal  of  the  American  Medical  Associa- 
tion, Vol.  64,  page  1539  (1915)- 

Mitchell.  Feeding  Experiments  on  the  Substitution  of  Protein  by 
Definite  Mixtures  of  Isolated  Amino  Acids.  Journal  of  Biological 
Chemistry,  Vol.  26,  page  231  (1916). 


68  CHEMISTRY  OF  FOOD  AND   NUTRITION 

Osborne.    The  Vegetable  Proteins. 

Osborne.  Die  Pflanzenproteine.  Ergehnisse  der  Physiologie,  Vol.  lo, 
pages  47-215  (iQio)- 

Osborne  and  Mendel.  Feeding  Experiments  with  Isolated  Food  Sub- 
stances. Carnegie  Institution  of  Washington,  Publication  No.  156 
(Parts  I  and  II)  and  a  series  of  subsequent  articles :  Journal  0}  Biological 
Chemistry,  Vol.  12,  page  473;  Vol.  13,  page  233;  Vol.  17,  page  325;  Vol. 
18,  page  i;  Vol.  20,  page  351;  Vol.  22,  page  241;  Vol.  25,  page  i; 
Vol.  26,  pages  I,  293;  Vol.  29,  page  69  (1911-1916).  Examine  also 
the  later  issues  of  this  Journal  for  papers  published  Subsequently  to 
the  compiling  of  this  list. 

Osborne,  Van  Slyke,  Leavenworth,  and  Vinograd.  Some  Products 
of  Hydrolysis  of  Gliadin,  Lactalbumin,  and  the  Protein  of  Rice.  Jour- 
nal of  Biological  Chemistry,  Vol.  22,  page  259  (1915). 

Plimmer.    Chemical  Constitution  of  the  Proteins,  I  and  II. 


CHAPTER  IV 

ENZYMES   AND   DIGESTION 

The  carbohydrates,  fats,  and  proteins  as  they  exist  in  foods* 
are  in  most  cases  not  of  a  nature  to  be  used  by  the  body  tissues 
in  the  exact  form  in  which  they  are  eaten,  but  must  usually 
undergo  more  or  less  alteration  in  the  digestive  tract  to  fit  them 
for  absorption  and  utihzation.  In  so  far  as  the  changes  which 
the  food  undergoes  in  the  alimentary  tract  are  chemical  they 
are  brought  about  mainly  by  the  action  of  digestive  enzymes ; 
but  the  efficiency  of  the  digestive  process  is  also  largely  de- 
pendent upon  the  mechanical  factors  of  digestion  which  there- 
fore will  also  be  briefly  considered  in  this  chapter. 

Historical 

The  idea  that  changes  comparable  to  fermentation  are  in- 
volved in  the  processes  of  digestion  apparently  originated  with 
von  Helmont  about  300  years  ago.  Sylvius,  half  a  century 
later,  cited  alcoholic  and  acetous  fermentations  to  illustrate  the 
type  of  process  by  which  he  believed  the  foodstuffs  to  be  digested. 
Descartes  held  that  as  the  result  of  a  peculiar  fermentation  there 
was  generated  in  the  stomach  ''an  acid  of  great  potency,  com- 
parable to  nitric  acid."  From  the  standpoint  of  our  present 
knowledge  these  early  scientists  appear  to  have  made  con- 
siderable progress  toward  a  correct  interpretation  of  the  digestive 
process;   but  in  their  own  times,  before  the  beginning  of  the 

*  A  table  showing  percentages  of  proteins,  fats,  and  carbohydrates  in  foods  is 
given  in  Appendix  B. 

69 


70  CHEMISTRY  OF  FOOD  AND   NUTRITION 

scientific  development  of  organic  or  physiological  chemistry, 
the  views  which  they  advanced  appeared  hazy  and  unscientific 
compared  with  those  of  the  physiologists  who  were  studying 
digestion  from  the  mechanical  point  of  view  and  by  supposedly 
exact  methods.  Thus  Dr.  Archibald  Pitcairn  (1652-1713) 
proposed  to  explain  gastric  digestion,  "  without  the  aid  of  a 
Daemon  or  a  Stygian  Liquor,"  as  due  entirely  to  the  triturating 
action  of  the  stomach,  the  power  of  whose  muscular  walls  he 
estimated  as  "  equal  to  12,951  pounds  "  (Gamgee). 

The  view  that  the  digestion  of  food  in  the  stomach  is  due 
solely  to  the  mechanical  action  of  the  stomach  walls  was  refuted 
by  Reaumur,  working  with  birds,  and  by  Stevens,  who  experi- 
mented with  a  man  who  was  accustomed  to  swallow  small  stones 
and  regurgitate  them  at  will.  In  Stevens'  experiments  this  man 
swallowed  hollow  silver  balls  filled  with  food  and  perforated  to 
permit  access  of  the  gastric  juice  but  strong  enough  to  resist 
the  muscular  contractions  of  the  stomach  walls.  Food  thus 
introduced  was  found  to  undergo  digestion  in  the  stomach  al- 
though it  was  entirely  protected  from  the  triturating  action  of 
the  stomach  walls.  Furthermore  Stevens  found  that  gastric 
juice  obtained  from  a  dog  was  able  to  digest  meat  outside  of  the 
stomach.  At  about  the  same  time  Spallanzani  also  showed 
clearly  that  gastric  juice  can  act  outside  of  the  body.  In  addi- 
tion, he  pointed  out  its  antiseptic  properties  and  emphasized  the 
difference  between  the  digestive  process  and  that  of  alcoholic, 
acid,  or  putrefactive  fermentation.  About  fifty  years  after 
the  work  of  Spallanzani  came  the  classical  observations  (1825- 
1833)  of  Dr.  Beaumont  upon  Alexis  St.  Martin,  who,  as  the  result 
of  a  gunshot  wound,  was  left  after  recovery  from  his  injury 
with  a  gastric  fistula  which  permitted  both  the  collection  of 
human  gastric  juice  and  the  direct  observation  of  the  processes 
going  on  in  the  stomach  of  a  healthy  man  ''active,  athletic,  and 
vigorous,  exercising,  eating,  and  drinking,  Hke  other  healthy 
and  active  people."     Dr.  Beaumont's  full  and  interesting  ac- 


ENZYMES  AND   DIGESTION  yt 

count  of  his  experiments  with  St.  Martin  ^  greatly  extended 
the  knowledge  both  of  the  muscular  behavior  of  the  stomach 
and  of  the  conditions  governing  the  secretion  of  the  gastric 
juice  and  the  "  chymification  "  of  the  food  in  the  stomach.  The 
year  after  the  publication  of  Beaumont's  observations,  Eberle 
showed  2  that  by  extracting  the  mucous  membrane  of  the 
stomach  with  dilute  hydrochloric  acid  he  could  obtain  an 
artificial  juice  which  showed  the  same  digestive  action  which 
Spallanzani  and  Beaumont  had  observed  with  the  natural  se- 
cretion, and  two  years  later  Schwann  ^  concluded  that  gastric 
juice  owed  its  peculiar  activity  to  a  substance  presumably  dif- 
ferent from  any  substance  previously  known  and  to  which  he 
gave  the  name  pepsin.  Schwann  did  not  claim  to  have  isolated 
this  peculiar  substance  in  a  pure  state  but  did  effect  a  partial 
separation.  Subsequently  several  other  investigators  attempted 
to  isolate  pepsin. 

Attempts  to  Determine  the  Chemical  Nature  of  Enzymes  * 

In  1902  Pekelharing  prepared  what  has  generally  been  re- 
garded as  probably  the  purest  pepsin  of  which  we  have  record. 
This  product  contained  carbon,  hydrogen,  nitrogen,  and  sul- 
phur in  proportions  within  the  range  of  variation  found  among 
ordinary  proteins.f  It  also  behaved  like  ordinary  proteins  in 
the  xanthoproteic  test  and  Millon  reaction  and  in  showing  the 
presence  of  the  tryptophane  group. 

^  W.  Beaumont.  Experiments  and  Observations  en  the  Gastric  Juice  and  the 
Physiology  of  Digestion.     Plattsburg,  1833. 

2  Eberle.    Physiologic  der  Verdauung  nach  Versuchen.     Wiirzburg,  1834. 

3  Schwann.  Ueber  das  Wesen  der  Verdauungsprocesse.  Miiller's  Archiv,  1836, 
pages  90-138. 

*  Those  students  not  yet  familiar  with  the  names  of  the  common  enzymes 
should  perhaps  read  first  the  sections  on  classification  and  terminology  below. 

t  A  small  amount  of  chlorine  shown  by  Pekelharing 's  preparation  was  later 
found  by  Dezani  to  be  not  an  essential  constituent  but  probably  due  to  incomplete 
removal  of  the  hydrochloric  acid  with  which  pepsin  is  associated  in  the  gastric  juice. 


72  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Dezani,  in  19 lo,  carried  forward  the  work  upon  the  chemical 
nature  of  pepsin  by  preparing  what  was  believed  to  be  a  sub- 
stantial duplicate  of  Pekelharing's  product  and  submitting  this  to 
hydrolysis,  followed  by  search  for  individual  hydrolytic  products 
according  to  the  methods  which  had  recently  been  developed  in 
the  study  of  the  structure  of  the  proteins.  He  demonstrated  the 
presence  of  leucine,  tyrosine,  arginine,  histidine,  and  lysine  and 
also  found  evidence  of  other  amino  acids  which  the  limitations 
of  his  material  and  methods  did  not  permit  him  to  identify. 

Thus  pepsin  as  prepared  by  Pekelharing  and  by  Dezani  is  a 
nitrogenous  material  not  identical  with  any  other  known  sub- 
stance but  complying  with  the  criteria  of  our  present  concep- 
tion of  a  protein  in  elementary  composition,  in  color  reactions, 
and  especially  in  yielding  the  famihar  amino  acids  upon  hy- 
drolysis. Recent  studies  by  Aldrich  also  indicate  that  the 
chemical  nature  of  pepsin  is  that  of  a  protein. 

It  must  be  borne  in  mind  that  the  criteria  of  purity  usually 
applied  in  chemical  investigations  are  not  applicable  to  enzyme 
preparations  because  of  their  colloidal  nature  and  the  readi- 
ness with  which  their  characteristic  properties  are  destroyed. 
Yet  in  view  of  the  fact  that,  with  very  few  if  any  excep- 
tions, the  changes  by  which  the  organic  foodstuffs  are  pre- 
pared for  absorption  in  the  digestive  tract  and  are  utilized  in 
the  body  tissues  are  dependent  upon  the  presence  of  enzymes  the 
material  for  whose  synthesis  must  in  the  long  run  be  furnished 
by  food,  we  should  not  be  deterred  by  the  inherent  diflSculties 
and  uncertainties  of  the  subject  from  the  study  of  such  evidence 
regarding  the  chemical  nature  of  the  enzymes  as  can  be  obtained ; 
nor  are  we  at  present  quite  so  much  in  the  dark  as  the  state- 
ments in  most  textbooks  would  seem  to  indicate. 

Several  years  earher  than  Pekelharing's  work  on  pepsin,  Os- 
borne ^  had  published  an  investigation  of  the  chemical  nature 

1  T.  B.  Osborne.  Journal  of  the  American  Chemical  Society,  Vol.  17,  page  587 
(189s) ;  Vol.  18,  page  536  (1896). 


ENZYMES  AND  DIGESTION  73 

of  diastase  (malt  amylase),  which  may  be  regarded  as  marking 
the  beginning  of  our  modern  knowledge  in  this  field.  From  this 
work  it  appeared  that  the  enzymic  activity  is  a  property  of  a 
definite  fraction  of  the  protein  material  of  the  malt,  or  in  other 
words  that  the  enzyme  is  protein  in  its  chemical  nature.  Al- 
though criticized  by  some,  Osborne's  findings  have  been  con- 
firmed by  the  most  recent  investigations.  Since  space  permits 
here  only  the  discussion  of  those  enzymes  which  are  directly 
concerned  in  digestion,  the  reader  must  be  referred  to  the 
original  papers  for  an  account  of  Osborne's  methods  and  results. 

Of  the  two  amylases  concerned  in  the  digestive  process, 
ptyalin  of  saUva  and  amylopsin  of  the  pancreatic  juice,  only 
the  pancreatic  amylase  has  been  studied  by  modern  methods 
with  reference  to  its  chemical  nature. 

In  an  investigation  ^  in  which  the  attempts  at  purification 
were  guided  and  their  success  largely  judged  by  quantitative 
determinations  of  the  starch-digesting  action  of  the  products 
there  was  developed  a  method  of  purification  which  in  nu- 
merous independent  experiments  yielded  a  product  that  was 
not  only  extraordinarily  active  in-  the  hydrolysis  of  starch  but 
was  essentially  uniform  both  in  digestive  activity  and  in  chemi- 
cal nature.  This  result  strongly  suggests  that  the  product  was 
not  merely  an  indefinite  mixture  but  represented  at  least  some 
approximation  toward  an  actual  isolation  of  the  enzyme.  These 
preparations  show  the  composition  and  color  reactions  of 
t5^ical  proteins  and,  Hke  Osborne's  malt  amylase,  the  material 
when  heated  in  water  solution  yields  an  albumin  coagulum  and 
a  proteose  or  peptone  which  remains  in  solution.  Moreover,  on 
hydrolysis  the  material  yields  the  same  groups  of  amino  acids 
which  are  yielded  by  typical  proteins  such  as  casein,  which  it 
also  resembles  in  elementary  composition. 

While  the  chemical  nature  of  the  Hpases  of  the  digestive  tract 

^Journal  of  the  American  Chemical  Society,  Vol.  33,  page  1195;  Vol.  34,  page 
1 104;  Vol.  35,  page  1790. 


74  CHEMISTRY  OF  FOOD  AND   NUTRITION 

has  not  been  studied,  Falk  and  Sugiura  have  shown  that  the 
purified  lipase  preparations  made  from  castor  beans  are,  Hke 
the  proteases  and  amylases  above  mentioned,  essentially  pro- 
tein material.* 

The  materials  obtained  in  attempts  to  isolate  enzymes  are 
here  called  merely  products  or  preparations;  it  is  not  stated 
that  any  enzyme  has  been  perfectly  separated  and  purified.  As 
already  explained,  the  familiar  criteria  of  purity  are  not  appli- 
cable to  these  unstable  colloidal  substances.  It  is  possible  that 
the  enzymes  in  the  purified  preparations  mentioned  above  may 
still  be  mixed  with  considerable  amounts  of  other  substances, 
and  it  has  evon  been  suggested  that  the  protein  material  of 
which  the  above-mentioned  enzyme  preparations  are  chiefly 
composed  may  be  present  only  as  a  carrier  and  that  the  actual 
enzyme  may  be  a  substance  of  a  different  nature.  There  is, 
however,  no  direct  evidence  in  favor  of  this  suggestion.  The 
facts  now  available  make  it  altogether  probable  that  the  typical 
enzymes  concerned  in  the  utiHzation  of  the  foodstuffs  either  are 
modified  proteins  or  contain  protein  as  an  essential  component. 
In  this  case  the  food  protein  must  furnish  material  for  body 
enzymes  as  well  as  for  body  tissue. 

Classification  and  General  Properties  of  Enzymes 

The  word  "enzyme"  (from  the  Greek  "in  yeast")  was  intro- 
duced by  Kiihne  as  a  general  designation  for  the  substances 
formed  in  plants  or  animals  which  had  previously  been  called 

*  Recently  Falk  has  suggested  that  the  lipolytically  active  grouping  is  the 
tautomeric  enol-lactim  fonri  of  the  peptide  linking  which  becomes  inactive  on 
rearrangement  to  the  keto  form.  Experiments  testing  this  view  resulted  in  the  pro- 
duction of  lipolytically  active  substances  by  the  action  of  alkali  on  castor  bean 
globulin,  casein,  and  gelatin.  Further  confirming  evidence  was  obtained  on  study- 
ing the  ester-hydrolyzing  action  of  glycine,  glycyl-glycine,  and  hippuric  acid  at 
different  hydrogen  ion  concentrations.  Falk  holds  that  "given  a  definite  chemical 
grouping,  the  nature  of  which  has  been  indicated,  and  which  may  be  present  in 
different  classes  of  substances,  certain  definite  lipolytic  actions  will  result." 


/ 


ENZYMES  AND   DIGESTION  75 

"  soluble "  or  "  unorganized  "  ferments  to  distinguish  them 
from  ''  organized "  ferments  (fermentation  organisms).  As 
more  and  more  of  the  activities  previously  regarded  as  char- 
acteristic of  organisms  have  been  found  to  be  due  to  enzymes, 
the  conception  of  enzyme  action  has  broadened  until  now  the 
term  enzyme  is  applied  by  most  writers  to  all  organic  catalysts 
formed  in  plant  or  animal  cells.  Those  which  are  ordinarily  ty 
secreted  from  the  cell  and  exert  their  activities  outside  of  it 
(as  in  the  case  of  the  digestive  ferments)  are  sometimes  called 
extracellular  enzymes,  and  those  which  normally  perform  their 
functions  within  the  cells  in  which  they  are  formed  (as  in  yeast 
or  in  muscle  cells)  may  be  called  intracellular  enzymes  even 
though  it  be  possible  by  artificial  means  to  cause  them  to  act 
independently  of  Hving  matter.  Although  each  enzyme  is 
generally  supposed  to  be  a  definite  chemica;l  substance,  the 
identification  and  classification  of  enzymes  are  based  upon  the 
changes  which  they  bring  about.  Some  of  the  better-known 
groups  of  enzymes  are  as  follows :  , 

1.  The  hydrolytic  enzymes.  /r 
a.   Proteolytic  or  protein-splitting  enzymes. 

h.   Lipolytic  or  fat-sphtting  enzymes. 

c.  Amylolytic  or  starch-splitting  enzymes. 

d.  Sugar-spHtting  enzymes. 

2.  The  coagulating  enzymes,  such  as  thrombin  or  thrombase 
(the  fibrin  ferment),  and  rennin,  which  causes  the  clotting  of  milk. 

3.  The  oxidizing  enzymes,  or  "  oxidases  "  (which,  if  the  oxi- 
dation be  accompanied  by  a  splitting  off  of  amino  groups,  may 
be  called  "  deamidizing '^  or  "  deaminizing  "  enzymes). 

4.  The  reducing  enzymes  or  "  reductpes." 

5.  Those  which,  like  the  zymase  of  yeast,  produce  carbon 
dioxide  without  using  free  oxygen. 

6.  Enzymes  causing  a  breaking  down  of  a  larger  into  a  smal- 
ler molecule  of  the  same  composition,  as  in  the  production  of 
lactic  acid  from  glucose. 


76  CHEMISTRY  OF  FOOD  AND  NUTRITION 

7.  Enzymes  causing  chemical  rearrangement  without  break- 
ing down  of  larger  into  smaller  molecules,  "  mutases." 

Terminology  of  the  hydrolytic  enzymes.  —  Except  in  so  far 
as  some  familiar  enzymes  continue  to  be  known  by  their  old 
estabhshed  names  (pepsin,  rennin,  trypsin,  etc.),  scientific 
usage  now  generally  follows  the  suggestion  of  Duclaux  that 
each  hydrolytic  enzyme  be  designated  by  a  name  indicating  the 
kind  of  substance  on  which  it  acts,  together  with  the  sufiix  ase. 
Thus  starch-splitting  enzymes  are  called  amylases;  fat-spHtting 
enzymes,  lipases;  protein-splitting  enzymes,  proteases.  The 
name  showing  the  activity  of  the  enzyme  is  often  preceded  by 
an  adjective  to  indicate  its  source ;  e.g.  salivary  amylase  (ptya- 
lin),  pancreatic  amylase  (amylopsin).  Such  designation  does  not 
necessarily  imply  that  the  amylase  found  in  the  saliva  either  is  or 
is  not  the  same  substance  as  the  amylase  of  the  pancreatic  juice. 

In  discussions  of  enzyme  action  the  substance  on  which  the 
enzyme  acts  is  sometimes  called  the  substrate. 

Within  the  cell  producing  it  an  enzyme  often  exists  in  an 
inactive  form  known  as  the  zymogen  or  antecedent  of  the  active 
enzyme.  The  zymogen  may  be  stored  in  the  cell  in  the  form  of 
material  which  is  converted  into  active  enzyme  at  the  time  of 
secretion,  or  the  secretion  may  be  poured  out  with  the  zymogen 
not  yet  completely  changed  to  active  enzyme,  or  sometimes  in  a 
form  which  requires  the  presence  of  some  other  substance  in 
order  to  render  it  active.  In  this  case  the  latter  substance  is 
said  to  activate  the  enzyme. 

Influence  of  hydrogen  ion  concentration.  —  The  activity  of 
most  enzymes  is  largely  dependent  upon  the  exact  acidity  or 
alkalinity  of  the  medium.  This  is  now  usually  expressed  in 
terms  of  hydrogen  ion  concentration.  Thus  a  normal  solution 
of  hydrochloric  acid  would  contain,  if  the  HCl  were  completely 
ionized,  i  gram  of  hydrogen  ions  per  Hter ;  and  in  a  thousandth- 
normal  solution  in  which  the  ionization  actually  is  almost  com- 
plete (actually  about  99  per  cent  of  the  HCl  in  such  a  solution 


ENZYMES  AND  DIGESTION  77 

is  ionized  at  ordinary  temperatures)  the  concentration  of  hy- 
drogen ions  is  o.ooi  gram  per  hter  or  i  x  io~^.  Pure  water, 
according  to  the  usually  accepted  estimates,  has  a  hydrogen 
ion  concentration  of  i  x  lo"''  and  the  same  concentration  of 
hydroxyl  ions.  Thus  water  which  is  pure  and  strictly  neutral 
may  also  be  regarded  as  being  equivalent  to  a  ten-millionth - 
normal  acid  and  at  the  same  time  a  ten-million th-normal  alkah. 
In  order  to  avoid  cumbersome  numbers  Sorensen  has  proposed 
to  indicate  hydrogen  ion  concentration  by  writing  the  negative 
exponent  as  a  whole  number,  e.g.  in  the  case  of  pure  water 
Ph"^  =  7;0;  in  thousandth-normal  hydrochloric  acid  Ph"^  =  3.0. 
Thus  according  to  the  Sorensen  notation,  generally  indicated 
by  the  use  of  the  symbol  Ph"^,  a  number  lower  than  7  shows 
acidity  and  the  more  acid  the  solution  the  lower  the  number ; 
a  number  higher  than  7  shows  alkalinity  and  the  greater  the 
alkaUnity  the  higher  the  Ph"^  number,  since  this  is  the  negative 
exponent  of  the  hydrogen  ion  concentration. 

It  must  be  remembered  that  the  Sorensen  exponent,  or  Ph"*" 
number,  varies  with  the  hydrogen  ion  concentration  not  arith- 
metically but   logarithmically :   i  x  10"^  =  Ph"*"  6.0 ;   2  X  io~^ 

=  Pe+  5-7- 

^  The  hydrogen  ion  concentrations  most  favorable  to  the  action 
of  certain  well-known  enzymes  have  recently  been  measured 
with  the  fottowing  results : 

Enzyme  Optimum  H  Ion  Concentration  as  Ph+ 


Invertase  (Sucrase) 

4.4 

(Nelson) 

Pepsin       .     .     . 

i.S 

(Okada) 

Trypsin      .     .     . 

8.0-8.3 

when  acting  on  fibrin  (Long) 

Trypsin     .     ,     . 

S.6^.3 

when  acting  on  casein  (Long) 

Malt  amylase     . 

4.4 

(Sherman  and  Thgmas) 

% 

T. 

•    t , 

Activity  of  the  Digestive  Enzymes 

That  the   typical  digestive   enzymes  are  very  pronounced 
catalysts  may  be  judged  from  the  relatively  large  amounts  of 


78  CHEMISTRY  OF  FOOD  AND   NUTRITION 

material  which  they  are  capable  of  digesting  under  favorable 
conditions.  Thus  Hammarsten's  rennin  coagulated  400,000  to 
800,000  times  its  weight  of  casein;  Petit  described  a  pepsin 
powder  which  dissolved  500,000  times  its  weight  of  fibrin  form- 
ing 1000  times  its  weight  of  peptone ;  the  pancreatic  amylase 
preparation  of  Sherman  and  Schlesinger  digested  ^,000,000 
times  its  weight  of  starch  with  the  production  of  ^ioo,ooo  times 
its  weight  of  maltose.  i; 

A  catalyzer  is  usually  considered  to  alter  the  velocity  of  a 
reaction  but  not  to  initiate  it.  Thus  hydrogen  peroxide  de- 
composes spontaneously  into  water^^d  oxygen.  In  a  pure 
aqueous  solution  this  change  goes  on  slowly,  but  it  is  very  greatly 
accelerated  by  the  presence  of  a  minute  amount  of  colloidal 
platinum.  Blood  and  tissue  extracts  contain  enzymes  which 
accelerate  the  decomposition  of  hydrogen  peroxide  apparently 
in  much  the  same  way  as  does  platinum,  and  the  present  tend- 
ency is  to  regard  the  enzymes  generally  as  acting  quite  like  the 
inorganic  catalyzers  in  altering  by  their  presence  the  velocity 
of  certain  reactions.  Some  of  the  best-known  enzyme  actions, 
however,  fit  into  this  view  only  theoretically ;  for  if  the  enzyme 
be  considered  as  simply  accelerating  a  reaction  already  taking 
place,  it  must  also  be  considered  that  in  the  absence  of  the 
enzyme  the  reaction  is  so  slow  that  it  cannot  be  demonstrated. 

It  may  perhaps  be  asked  why,  if  enzymes  act  by  catalysis, 
there  should  be  any  limit  to  the  amount  of  substrate  which  the 
enzyme  can  hydrolyze.  One  reason  that  enzymes  cannot  hy- 
drolyze  infinite  amounts  of  substrate  is  that  they  are  them- 
selves unstable  organic  substances  which  undergo  decomposition 
when  kept  in  solution.  In  most  cases  the  purer  the  enzyme  the 
more  rapidly  its  solutions  lose  their  activity.  Another  reason 
that  an  enzyme  does  not  continue  to  hydrolyze"  substrate 
indefinitely  is  that  the  reaction  is  progressively  retarded  by 
the  accumulation  of  the  products  formed. 

The  activity  of  an  enzyme  may  be  stopped,  even  when  all 


ENZYMES  AND   DIGESTION 


79 


other  conditions  are  favorable,  by  the  accumulation  of  the  prod- 
uct of  its  action;  and  in  certain  circumstances  the  action  of 
the  enzyme  may  be  reversed  so  as  to  accelerate  a  change  in  the 
opposite  direction  to  that  in  which  it  ordinarily  acts.  Thus 
Croft  Hill  showed  it  to  be  possible  to  reverse  the  ordinary  action 
of  maltase  so  as  to  make  it  bring  about  a  conversion  of  mono- 
into  di-saccharide ;  Pottevin  synthesized  triolein  by  means  of 
the  pancreas  ferment,  and  Taylor  and  others  have  demonstrated 
a  partial  reversion  of  the  tryptic  digestion  of  proteins.  While 
the  exact  significance  of  these  experiments  upon  the  reversi- 
bility of  the  actions  brought  about  by  the  digestive  enzymes  has 
been  questioned,  there  seems  to  be  no  doubt  that  hydrolytic 
enzymes  are  widely  distributed  in  active  cells  and  that  many  of 
the  transformations  which  take  place  in  the  course  of  the  me- 
tabolism of  the  foodstuffs  in  the  body  are  best  explained  on  the 
ground  of  the  reversibility  of  enzyme  action.  Consideration  of 
the  tissue  enzymes  will  be  left  until  the  study  of  the  fate  of  the 
foodstuffs  in  metabolism  is  taken  up.  At  this  point  it  may 
be  convenient  to  summarize  in  tabular  form  the  occurrence 
and  action  of  the  chief  digestive  enzymes. 


Summary  of  Chief  Digestive  Enzymes 


Enzyi 

HES 

Where  Chiefly  Found 

Action 

Ptyalin     (salivary 

Salivary  secretions 

Converts  starch  to 

amylase) 

maltose 

Amylopsin 

(pan- 

Pancreatic  juice 

'Converts  starch  to 

creatic  amylase) 

maltose 

Invertase 

Intestinay$5ce 

ConvertT      sucrose 

Act  on  Car-  i 

(Sucrase) 

^ 

to    glucose    and 

bohyd  rates 

fructos^ 

Maltase 

Intestinal  juice  / 

Converts  maltose 
to  glucose 

Lactase 

Intestinal  juice 

Converts  lactose 
to  glucose  and 
galactose 

Lipases 

Gastric    ( ?)    and 

Split  fats  to  fatty 

Act  on  Fat    < 

pancreatic 

acids   and   glyc- 

juices 

erol 

\ 


8o 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


Summary  of  Chief  Digestive  Enzymes  (Continued) 
Enzymes  Where  Chiefly  Found  [Action 


Act  on  Pro- 
teins 


Pepsin 


Trypsin 


Erepsin 


Gastric  juice 
Pancreatic  juice 

Intestinal  juice 


Splits  proteins  to 
proteoses  and 
peptones 

Splits  proteins  to 
proteoses,  pep- 
tones, polypep- 
tids,  and  amino 
acids 

Splits  peptones  to 
amino  acids  and 
ammonia 


With  this  brief  sketch  of  the  nature  and  action  of  the  diges- 
tive enzymes,  the  adequate  discussion  of  which  would  require 
a  volume  in  itself,  we  may  now  pass  to  a  review  of  the  digestive 
process,  following  the  course  of  the  food  through  the  human 
aHmentary  tract  and  noting  briefly  both  the  mechanical  and 
chemical  treatment  to  which  it  is  subjected. 

Salivary  and  Gastric  Digestion 

Since  the  muscular  movements  of  the  digestive  tract,  par- 
ticularly of  the  stomach  when  empty,  play  an  important  part 
in  bringing  about  the  sensations  which  lead  to  the  taking  of 
food,  it  may  be  well  to  note  at  this  point  the  results  obtained 
by  Cannon  and  Washburn  in  their  recent  investigation  of 
hunger.  Lest  hunger  be  confused  with  appetite,  it  is  essential 
to  clearness  that  these  terms  be  defined.  Some  consider  that 
the  two  experiences  differ  only  quantitatively,  appetite  being 
regarded  as  a  mild  state  of  hunger;  but  Cannon  and  Wash- 
burn hold  that  hunger  and  appetite  are  fundamentally  differ- 
ent.    In  their  view : 

**  Appetite  is  related  to  previous  sensations  of  the  taste  and 
smell  of  food ;  it  has  therefore,  as  Pawlow  has  shown,  important 
psychic  elements.  It  may  exist  separate  from  hunger,  as,  for 
example,  when  we  eat  delectable  dainties  merely  to  please  the 


ENZYMES  AND  DIGESTION  8l 

palate.  Sensory  associations,  delightful  or  disgusting,  deter- 
mine the  appetite  for  any  edible  substance,  and  either  memory 
or  present  stimulation  can  thus  arouse  desire  or  dislike  for 
food." 

"  Hunger,  on  the  other  hand,  is  a  dull  ache  or  gnawing  sen- 
sation referred  to  the  lower  midchest  region  or  epigastrium. 
It  is  the  organism's  first  strong  demand  for  nutriment,  and,  not 
satisfied,  is  likely  to  grow  into  a  highly  uncomfortable  pang, 
less  definitely  localized  as  it  becomes  more  intense.  It  may 
exist  separate  from  appetite,  as,  for  example,  when  hunger  forces 
the  taking  of  food  not  only  distasteful  but  even  nauseating." 

Hunger  is  not  due  merely  to  emptiness  of  the  stomach.  It 
is  true  that  under  ordinary  conditions  hunger  is  apt  to  appear 
soon  after  the  last  food  has  passed  from  the  stomach  to  the  in- 
testine, but  if  the  stomach  be  artificially  emptied,  the  sensation 
of  hunger  may  not  be  felt  until  some  hours  afterward.  Nor  is 
hunger  due  to  hydrochloric  acid  secreted  into  an  empty  stomach, 
for  if  the  empty  stomach  of  a  hungry  person  be  washed  out,  but 
little  if  any  acid  is  found. 

The  explanation  of  hunger ,  advanced  by  Cannon  and  Wash- 
burn, is  that  it  is  due  to  the  muscular  contractions  of  the  walls 
of  the  empty  stomach. 

In  order  to  learn  whether  direct  proof  of  this  might  be  secured  experi- 
mentally in  man,  one  of  the  investigators  accustomed  himself  to  swallowing 
a  small  soft  rubber  balloon  attached  to  the  end  of  a  rubber  tube  by  means 
of  which  it  could  be  withdrawn  when  desired.  The  tube  and  bulb  were 
habitually  carried  thus  in  the  esophagus  and  stomach  for  two  or  three 
hours  at  a  time  until  the  experience  ceased  to  have  any  disturbing  effect. 
Experiments  were  then  made  in  which  the  balloon,  thus  held  in  the  stomach, 
was  partially  inflated  with  air  and  connected  with  a  manometer  and  record- 
ing apparatus  by  means  of  which  any  pressure  exerted  upon  the  balloon  was 
recorded  automatically.  In  the  actual  experiments,  the  subject  sat  at  rest 
i  with  his  hand  on  a  key  which  he  pressed  whenever  he  experienced  the  sensa- 
\  tion  of  hunger.  This  key  was  connected  with  a  recording  device  which, 
I  like  the  apparatus  recording  the  muscular  contractions  of  the  stomach  upon 
I  the  rubber  balloon,  was  out  of  sight  of  the  subject. 


82  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Before  hunger  was  experienced  the  recording  apparatus  revealed  no  evi- 
dence of  muscular  activity  in  the  stomach.  The  records  of  hunger  "pangs" 
and  of  muscular  contractions  of  the  stomach  were  always  approximately 
simultaneous,  that  is,  when  the  subject  of  the  experiment  felt  hungry,  power- 
ful contractions  of  the  stomach  were  always  being  registered.  The  con- 
tractions were  about  30  seconds  in  duration,  with  pauses  of  30  to  90  seconds 
between.  It  was  found  in  almost  every  case  that  the  contraction  reached 
its  greatest  intensity  just  before  the  record  of  the  hunger  sensation  began, 
and  that  the  feeling  of  hunger  disappeared  when  the  contraction  ceased 
although  no  food  or  drink  had  been  taken.  Cannon  considers  the  evidence 
conclusive  that  hunger  is  caused  by  the  contractions,  and  not  vice  versa, 
as  Boldireff  had  thought.  Other  observations  in  the  course  of  Cannon's 
experiments  showed  that  the  lower  end  of  the  esophagus  also  contracts 
periodically  in  hunger,  an  explanation  of  the  fact  that  sensations  of  hunger 
may  be  felt  in  cases  where  the  stomach  has  been  removed.  Furthermore 
Cannon  considers  that  vague  sensations  of  hunger  may  also  originate  from 
muscular  contractions  in  the  intestine. 

What  causes  the  stomach  contractions  which  give  the  sen- 
sation of  hunger  has  not  been  determined.  They  do  not  seem 
to  be  directly  related  to  bodily  need.  That  they  usually  begin 
at  or  soon  after  the  accustomed  meal  hour  may  be  taken  not 
only  as  evidence  that  habit  plays  an  important  role,  but  also 
as  an  indication  of  the  desirability  of  eating  at  regular  times ; 
for  in  view  of  the  importance  of  the  muscular  tone  of  the  stomach 
walls,  these  observations  seem  to  justify  the  view  that  the  strong 
muscular  contraction  of  the  empty  stomach  may  be  regarded 
as  an  indication  that  the  condition  which  causes  the  first  sen- 
sation of  hunger  is  that  in  which  the  stomach  is  in  the  best  state 
of  readiness  to  receive  the  food.  There  is  also  direct  experi- 
mental evidence  that  the  stomach  digests  more  expeditiously 
the  food  which  is  "  eaten  with  hunger  "  (Hudek  and  Stigler, 
cited  by  Carlson).  The  description  of  the  digestive  process 
which  follows  presupposes  that  the  food  is  eaten  under  favor- 
able conditions  and  received  by  a  digestive  tract  which  has  been 
permitted  to  form  good  and  regular  habits. 

The  eating  of  food  induces  a  flow  of  saliva  from  great  numf- 


ENZYMES  AND  DIGESTION  83 

bers  of  minute  glands  in  the  lining  membrane  of  the  mouth 
and  from  the  three  pairs  of  large  salivary  glands.  That  saliva 
is  secreted  in  response  to  psychic  as  well  as  chemical  stimulation 
is  shown  by  the  fact  that  actual  contact  with  the  food  is  not 
necessary,  since  secretion  may  be  started  by  the  sight  or  odor 
or  even  the  thought  of  food.  Mixed  human  saliva  has  usually 
a  faintly  alkaline  reaction  and  always  contains  ptyalin  (salivary 
amylase),  although  its  amylolytic  power  appears  to  vary  con- 
siderably with  individuals  and  with  the  same  individual  at  dif- 
ferent times  of  the  day.  As  the  food  comes  in  contact  with 
saHva,  the  digestion  of  starch  and  dextrin  under  the  influence  of 
the  ptyalin  begins  at  once ;  but  as  mastication  is  an  entirely 
voluntary  act,  the  thoroughness  with  which  the  food  becomes 
mixed  with  saliva  is  subject  to  wide  variations. 

Usually  the  food  stays  too  short  a  time  in  the  mouth  for  the 
starch  to  be  acted  upon  there  to  any  great  extent,  and  until 
recently  it  was  supposed  that  salivary  digestion  must  cease 
almost  as  soon  as  the  food  reaches  the  stomach,  since  the  ac- 
tivity of  ptyalin  is  quickly  checked  by  even  small  amounts  of 
free  hydrochloric  acid.  >  It  was  supposed  that  the  food  mass 
must  soon  be  mixed  with  the  gastric  juice  under  the  influence 
of  the  "  churning  "  of  the  stomach  contents  by  the  muscular 
contraction  of  the  stomach  walls,  which  was  so  interestingly 
described  by  Dr.  Beaumont  in  the  account  of  his  classical  re- 
searches already  referred  to  (pages  70-7 1 ) .  From  the  nature  of  the 
case  Dr.  Beaumont's  observations  were  made  entirely  at  one  point 
in  the  stomach.  Here  he  found  during  digestion  a  vigorous  mus- 
cular churning  and  mixing  of  the  food  mass  with  the  gastric  juice. 
For  a  long  time  this  was  supposed  to  represent  the  state  of  the 
entire  stomach  contents.  This  view  has  now  been  abandoned  as 
the  result  of  a  number  of  recent  investigations,  among  which 
those  of  Cannon  and  of  Griitzner  are  of  especial  interest. 

When  a  small  amount  of  an  inert  metallic  compound  such  as 
bismuth  subnitrate  is  mixed  with  the  food,  it  becomes  possible 


84 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


to  photograph  the  food-mass  within  the  body  by  means  of  the 
Roentgen  rays.  By  the  use  of  this  method  Cannon  has  carried 
out  an  extended  series  of  observations  upon  the  movements  of 
the  stomach  and  intestines  during  digestion,^  upon  the  results 
of  which  the  statements  concerning  the  mechanism  of  digestion 
in  this  chapter  are  chiefly  based. 

Cannon's  observations,  confirmed  by  those  of  other  investi- 
gators, show  that  the  vigorous  muscular  movements  described 

by  Beaumont,  and  which  gen- 
erally begin  20  to  30  minutes 
after  the  beginning  of  a  meal, 
occur  only  in  the  middle  and 
posterior,  or  pyloric,  portion  of 
the  stomach,  while  the  anterior 
portion,  or  fundus,  which  serves 
as  a  reservoir  for  the  greater 
portion  of  the  food,  is  not  ac- 
tively concerned  in  these  move- 
ments and  does  not  rapidly  mix 
its  contents  with  the  gastric 
juice. 

That  there  is  no  general  circu- 
lation and  mixing  of  the  entire 
stomach  contents  during  or  immediately  following  a  meal  is 
further  shown  by  the  experiments  of  Griitzner,  who  fed  rats 
with  foods  of  different  colors  and  on  killing  the  animals  and 
examining  the  stomach  contents  found  that  the  portions  which 
had  been  eaten  successively  were  arranged  in  definite  strata. 
The  food  which  had  been  first  eaten  lay  next  to  the  walls  of  the 
stomach  and  filled  the  pyloric  region,  while  the  succeeding  por- 
tions were  arranged  regularly  in  the  interior  in  a  concentric 
fashion  (Fig.  5).     In  describing  this  result  Howell  says:  "  Such 

1  These  and  other  investigations  are  fully  discussed  in  Cannon's  Mechanical 
Factors  in  Digestion.    See  also  Carlson's  Control  of  Hunger  in  Health  and  Disease. 


Fig.  5.  —  Section  of  frozen  stomach 
of  rat  during  digestion  to  show  the 
stratification  of  food  given  at  differ- 
ent times.  {Griitzner.)  The  food 
was  given  in  three  portions  and 
colored  differently.  Reproduced  from 
Howell's  Textbook  of  Physiology,  by 
permission  of  the  W.  B.  Saunders  Co. 


ENZYMES  AND  DIGESTION  85 

an  arrangement  of  the  food  is  more  readily  understood  when 
one  recalls  that  the  stomach  has  never  any  empty  space  within ; 
its  cavity  is  only  as  large  as  its  contents,  so  that  the  first  portion 
of  food  eaten  entirely  fills  it,  and  successive  portions  find  the 
wall  layer  occupied  and  are  therefore  received  into  the  interior." 

The  character  of  the  gastric  juice  secreted  in  different  parts 
of  the  stomach  varies  considerably,  especially  as  regards  its 
acidity.  In  the  middle  region  the  secretion  is  rich  in  acid, 
while  both  in  the  cardiac  region  and  at  the  extreme  pyloric  end, 
the  "  border  cells  "  or  "  cover  cells  "  (from  which  the  secretion 
of  the  acid  appears  to  take  place)  are  few  in  number  or  entirely 
lacking,  and  the  juice  secreted  in  these  regions  may  be  neutral 
or,  according  to  Howell,  even  slightly  alkaline.^ 

The  nature  and  extent  of  the  muscular  movements  also  vary 
greatly  in  the  different  regions  of  the  stomach.  The  peristaltic 
waves  of  muscular  constriction  which  bring  about  the  thorough 
mixing  of  the  food  with  the  gastric  juice  begin  in  the  middle 
region  and  travel  toward  the  pylorus.  Over  the  pyloric  part 
of  the  stomach  when  food  is  present  constriction  waves  are 
continually  coursing  toward  the  pylorus.  The  food  in  this  region 
is  first  pushed  forward  by  the  running  wave  and  then  by  pres- 
sure of  the  stomach  wall  is  returned  through  the  ring  of  con- 
striction. Thus  the  food  in  this  portion  of  the  stomach  is 
thoroughly  mixed  with  the  gastric  juice  and  is  forced  by  an 
oscillating  progress  toward  the  pylorus. 

The  food  in  the  cardiac  end  of  the  stomach  is  not  moved  by 
peristalsis,  and  so  comes  only  slowly  into  contact  with  the 
gastric  juice;  and  since  the  juice  secreted  here  contains  little 
if  any  free  acid,  a  large  part  of  the  food  mass  remains  for  some 
time  (variously  estimated  at  from  30  minutes  to  2  hours  or 
more)  in  approximately  the  same  neutral  or  faintly  alkaUne 
condition  in  which  it  was  swallowed,  and  salivary  digestion 
continues  in  this  part  of  the  stomach  without  interruption. 
Thus,  if  the  food  has  been  thoroughly  chewed  and  well  mixed 


86  CHEMISTRY  OF  FOOD  AND   NUTRITION 

with  saliva  before  swallowing,  much  if  not  most  of  its  starch 
may  be  converted  into  dextrin  and  maltose  in  the  cardiac  region 
of  the  stomach  before  the  activity  of  the  ptyalin  is  stopped  by 
contact  with  the  acid  of  the  gastric  juice. 

The  fundus,  however,  is  not  entirely  inactive,  but  acts  as  a 
sort  of  elastic  pouch  which  is  distended  by  and  slowly  con- 
tracts upon  the  food  mass,  thus  gradually  tending  to  move  the 
posterior  portions  and  particularly  the  more  fluid  portion  into 
the  pyloric  region.  As  digestion  proceeds,  the  pylorus  opens 
more  frequently  and  the  stomach  tends  to  empty  itself  more 
and  more  freely,  until  finally  the  pylorus  may  open  to  allow 
the  passage  of  particles  which  have  not  been  acted  upon  by 
the  gastric  juice.  Whether  the  stomach  will  thus  completely 
empty  itself  of  one  meal  before  the  eating  of  the  next  will  de- 
pend of  course  upon  the  length  of  the  interval  and  the  amount 
and  character  of  the  food  composing  the  meal.  Small  test 
meals  may  disappear  in  from  i  to  4  hours,  but  meals  approxi- 
mating one  third  of  the  day's  food  may  not  disappear  entirely 
from  the  stomach  during  6  or  7  hours. 

In  studying  the  passage  of  food  from  the  stomach  into  the  in- 
testine, Cannon  found  that  the  pylorus  does  not  open  at  the 
approach  of  each  wave  of  constriction  which  passes  over  this 
part  of  the  stomach,  but  only  at  irregular  intervals.  When  the 
observations  made  by  means  of  the  Roentgen  rays  were  sup- 
plemented by  chemical  examinations  of  stomach  and  intestinal 
contents  removed  at  different  stages,  it  appeared  that  the 
presence  of  free  acid  in  the  pyloric  part  of  the  stomach  causes 
the  pylorus  to  open,  and  its  presence  in  the  small  intestine 
causes  the  pylorus  to  close.  Thus  it  would  appear  that  under 
normal  conditions  it  is  only  when  the  protein  of  the  food  has 
become  more  or  less  completely  saturated  with  hydrochloric 
acid  and  some  of  the  latter  remains  in  the  free  state,  that  the 
food  is  allowed  to  pass  into  the  intestine. 

Ordinarily,  when  each  is  fed  separately,  protein  food  stays 


ENZYMES  AND  DIGESTION  87 

longer  in  the  stomach  than  carbohydrate,  fat  longer  than  pro- 
tein, and  mixtures  of  fat  and  protein  leave  the  stomach  more 
slowly  than  either  alone.  This  is  probably  because  fat  tends  to 
retard  both  the  motihty  of  the  stomach  and  the  secretion  of  the 
acid  gastric  juice.  In  general  the  softer  or  more  fluid  the  fat 
the  more  rapidly  it  will  leave  the  stomach ;  also  emulsified  fats 
tend  to  pass  on  more  promptly  than  fat  of  the  same  kind  taken 
in  larger  masses. 

The  difference  noted  between  protein  and  carbohydrate  is 
doubtless  due  to  the  fact  that  combination  of  the  acid  of  the 
gastric  juice  with  the  protein  of  the  food  delays  the  appearance 
of  free  acid  at  the  pylorus ;  for  when  protein  food  was  acidulated 
before  feeding  and  carbohydrate  food  was  made  alkaline,  the 
protein  was  found  to  leave  the  stomach  more  rapidly  than  the 
carbohydrate.  That  the  passage  of  food  from  stomach  to 
intestine  is  governed  mainly  by  the  degree  of  acidity  reached 
in  the  pyloric  part  of  the  stomach  is  of  interest  in  view  of  the 
importance  to  the  organism  of  the  action  of  the  acidity  of  the 
gastric  juice  in  effecting  a  partial  disinfection  of  the  food.  It 
has  been  found  that  when  through  any  cause  the  hydrochloric 
acid  of  the  gastric  juice  is  abnormally  decreased,  the  numbers 
of  bacteria  in  the  stomach  contents  may  increase  greatly.  It 
will  be  seen  also  that  the  acidity  of  the  chyme  as  it  passes 
the  pylorus  has  an  important  influence  upon  the  secretion  of 
the  pancreatic  juice. 

The  most  important  characteristics  of  gastric  juice  are  the 
presence  of  free  hydrochloric  acid  and  of  pepsin.  While  other 
acids  may  be  found  in  stomach  contents,  the  acidity  of  gastric 
juice  appears  to  be  due  entirely  to  hydrochloric  acid.  Normal 
human  gastric  juice  has  been  found  by  different  observers  to 
contain   about  0.2  to  0.4  per  cent  of  free  hydrochloric  acid.* 

♦According  to  Carlson,  "hunger  juice"  and  "appetite  juice"  in  man  contain 
respectively  0.25  per  cent  and  0.40  per  cent  of  free  hydrochloric  acid  —  averages  of 
hundreds  of  observations  upon  a  healthy  man  having  a  gastric  fistula. 


88  CHEMISTRY  OF  FOOD  AND  NUTRITION 

The  stimuli  which  bring  about  secretion  of  gastric  juice  are 
both  psychical  and  chemical. 

Psychical  stimulation  results  from  the  sensations  of  eating  and  may  also 
be  due  to  the  sight  and  odor  of  food.  The  psychical  secretion  is  studied 
chiefly  by  means  of  the  "fictitious  feeding"  ("sham  feeding")  experiments 
in  which  food  is  given  to  dogs  which  have  been  prepared  with  esophageal 
openings  through  which  the  swallowed  food  escapes  without  entering  the 
stomach.  When  such  a  dog  is  fed  with  meat,  for  example,  there  is  a  con- 
siderable secretion  of  gastric  juice  in  spite  of  the  fact  that  no  food  reaches 
the  stomach.  Such  a  flow  of  gastric  juice  is  due  to  impulses  received  through 
the  nervous  system  and  specifically  through  the  vagus  nerve,  for  fictitious 
feeding  has  been  found  to  cause  a  flow  of  gastric  juice  when  the  vagi  are 
intact,  but  not  after  they  have  been  cut.  Secretion  produced  in  this  way 
reflexly  as  the  result  of  the  sensation  of  taste,  odor,  etc.,  is  called  by  Pawlow 
a  "psychic  secretion"  or  "appetite  juice."  When  the  secretion  is  once 
started,  even  if  no  food  enters  the  stomach,  the  flow  of  juice  may  continue 
for  some  time  after  the  stimulus  has  ceased. 

On  the  other  hand,  the  normal  secretion  of  gastric  juice  may  be  checked 
by  unpleasant  feelings  such  as  fear,  anger,  or  pain.  This  has  been  repeatedly 
observed  with  frightened  or  angry  animals.  Hornborg  reports  a  similar 
observation  upon  a  small  boy.  Food  was  shown  but  withheld,  and  the  child 
became  vexed  and  distressed,  whereupon  no  gastric  juice  was  secreted.  After 
he  was  calmed,  and  given  the  food,  it  was  some  time  before  secretion  began. 
Cannon  infers,  furthermore,  that  there  is  a  "psychic  tone"  or  "psychic 
contraction"  of  the  gastro-intestinal  muscles,  analogous  to  the  psychic 
secretion.  In  the  same  fashion  that  secretion  may  be  checked,  so  also  the 
movements  of  the  stomach,  bringing  about  the  mixing  of  food  with  gastric 
juice  and  insuring  its  passage  on  into  the  duodenum,  may  be  stopped  during 
excitement  or  pain.  This  fact  has  been  observed  many  times  in  experi- 
ments with  various  animals,  as  well  as  in  the  case  of  human  beings. 

If  psychic  secretion  is  normally  excited,  it  insures  the  prompt 
beginning  of  gastric  digestion.  Stimulations  arising  within  the 
stomach  itself  supplement  the  psychic  influences  and  provide 
for  the  continued  secretion  of  the  gastric  juice  long  after  the 
mental  effects  of  a  meal  have  disappeared.  This  second  stimu- 
lation is  chemical  and  depends  upon  the  production  in  the  py- 
loric mucous  membrane  of  a  specific  substance,  or  hormone, 
which  acts  as  a  chemical  messenger  to  all  parts  of  the  stomach, 


ENZYMES  AND  DIGESTION  89 

being  absorbed  into  the  blood  and  thence  exciting  the  activity 
of  the  various  secreting  cells  of  the  gastric  glands  (Stariing). 
Meat  extracts,  soups,  etc.,  are  particularly  active  in  exciting 
the  secretion  which  depends  upon  chemical  stimulation;  milk 
causes  less  secretion ;  white  of  egg  is  said  to  have  no  effect. 

Under  normal  conditions,  the  amount  of  nutritive  material 
absorbed  from  the  stomach  is  insignificant  as  compared  with 
the  amount  absorbed  from  the  intestine.  Nearly  all  the  food 
eaten  is  passed  from  the  stomach  into  the  intestine  in  the  form 
of  chyme,  having  been  more  or  less  perfectly  hquefied  and  acid- 
ulated by  its  thorough  mixing  with  the  gastric  juice  in  the  middle 
and  pyloric  regions  of  the  stomach. 

The  stomach  therefore  has  several  functions.  It  serves  (i) 
as  a  storage  reservoir  receiving  food  in  relatively  large  quanti- 
ties, say  three  times  a  day,  and  passing  it  on  to  the  intestine  in 
small  portions  at  frequent  intervals,  (2)  as  a  place  for  the  con- 
tinuation of  the  salivary  digestion  of  starch,  and  (3)  for  the 
beginning  of  the  digestion  of  proteins  and  perhaps  fats,  and 
finally  (4)  as  a  disinfecting  station  by  virtue  of  the  germicidal 
action  of  the  hydrochloric  acid  of  the  gastric  juice. 


Intestinal  Digestion 

Digestion  in  the  small  intestine.  —  When  the  pylorus  opens, 
food,  now  reduced  to  Hquid  chyme,  is  projected  into  the  upper 
part  of  the  small  intestine,  where  it  usually  lies  for  some  time 
in  the  curve  of  the  duodenum,  until  several  additions  have 
been  made  to  it  from  the  stomach.  While  the  food  rests  here 
the  bile  and  pancreatic  juice  are  poured  out  upon  it,  and  here 
also,  as  well  as  in  other  parts  of  the  small  intestine,  a  certain 
amount  of  intestinal  digestive  juice  ("  succus  entericus ") 
is  secreted  by  the  glands  of  the  lining  membrane  and  mixed 
with  the  intestinal  contents.  ^  While  for  purposes  of  descrip- 
tion the  pancreatic  and  intestinal  juices  and  the  bile  may  be 


go  CHEMISTRY  OF  FOOD  AND  NUTRITION 

discussed  separately,  it  is  to  be  remembered  that  in  normal 
digestion  they  always  act  together.  Cannon's  observations 
showed  that  after  a  certain  amount  of  food  and  digestive 
juices  has  accumulated  as  just  described  in  the  first  loop  of 
the  small  intestine,  the  mass  all  at  once  becomes  segmented 
by  constrictions  of  the  intestinal  walls,  and  the  segmentation 
is  repeated  rhythmically  for  several  minutes,  so  that  the  in- 
dividual portions  are  subjected  to  relatively  extensive  and 
energetic  to-and-fro  movement,  which  is  doubtless  very  im- 
portant in  facilitating  the  emulsification  of  fat.  Other  effects 
of  the  muscular  constrictions  which  cause  the  segmentation  are 
(i)  a  further  mixing  of  food  and  digestive  juiceg,  (2)  the  bring- 
ing of  the  digested  food  into  contact  with  the  absorbing  mem- 
brane, (3)  the  emptying  of  the  venous  and  lymphatic  radicles 
in  the  membrane,  the  material  which  they  have  absorbed  being 
forced  into  the  veins  and  lymph  vessels  by  the  compression  of 
the  intestinal  wall.  After  a  varying  length  of  time  the  seg- 
mentation ceases  and  the  small  segments  are  carried  forward 
individually  by  the  peristaltic  movement,  or  join  and  move  on 
as  a  single  body. 

The  fluid  food  mass  which  the  stomach  pours  into  the  duo- 
denum contains  a  small  amount  of  free  hydrochloric  acid  be- 
,  sides  a  larger  amount  combined  with  protein  and  sometimes  or- 
!  ganic  acids  from  the  food  as  eaten,  or  from  bacterial  fermentation 
of  carbohydrates  in  the  stomach.  The  pylorus  having  closed, 
the  alkaUnity  of  the  bile,  the  pancreatic  juice,  and  the  intestinal 
juice  combine  to  neutralize  the  acids  present. 

In  man  the  main  duct  of  the  pancreas  and  the  bile  duct  unite 
and  empty  into  the  small  intestine  about  8  to  10  cm.  (3  to  4 
inches)  below  the  pylorus.  The  pancreatic  juice  is  a  clear  liquid 
having  an  alkaHnity  probably  equivalent  to  a  0.5  per  cent 
solution  of  sodium  carbonate  and  containing  three  important 
enzymes  or  their  zymogens  —  trypsin,  amylopsin  (amylase), 
and  steapsin  or  lipase. 


ENZYMES  AND  DIGESTION  91 

The  outflow  of  the  pancreatic  juice  begins  at  once  when  any 
of  the  acid  stomach  contents  passes  through  the  pylorus,  and 
has  been  shown  by  Bayliss  and  Starling  to  be  due  to  a  definite 
chemical  substance,  secretin,  a  typical  hormone  produced  as 
the  result  of  the  action  of  the  acid  upon  some  constituent  of 
the  intestinal  mucous  membrane,  which  is  absorbed  and  carried 
by  the  blood  to  the  pancreas  and  there  stimulates  the  flow  of 
pancreatic  juice. 

Human  bile,  which,  as  already  stated,  enters  the  intestine 
through  the  same  duct  with  the  pancreatic  juice,  is  a  sHghtly 
alkaline  solution  containing,  in  addition  to  water  and  salts, 
bile  pigments,  bile  acids  (as  salts),  cholesterin,  lecithin,  and  a 
peculiar  protein  derived  from  the  mucous  membrane  of  the 
bile  ducts  and  gall  bladder.  The  presence  of  the  bile  in  the 
intestinal  contents  greatly  increases  the  solubility  of  the  fatty 
acids,  while  at  the  same  time  it  diminishes  the  surface  tension 
Between  watery  and  oily  fluids.  Bile  may  also  accelerate  the 
action  of  pancreatic  lipase  in  a  more  direct  way.  Thus  bile 
aids  both  the  digestion  and  the  absorption  of  fats.  The  bile 
acids  are  themselves  absorbed  to  a  considerable  extent  and 
again  secreted  by  the  liver.  The  secretion  of  bile  by  the  liver, 
although  variable  in  amount,  is  continuous.  Its  ejection  from 
the  gall  bladder  into  the  intestine  occurs,  however,  only  during 
digestion,  and  appears  to  be  excited  by  the  passage  of  chyme 
through  the  pylorus,  and  to  run  parallel  to  the  outpouring  of 
the  pancreatic  juice.  According  to  StarHng,  the  rapid  flow  of 
bile  during  intestinal  digestion  is  due  not  only  to  the  pouring 
out  of  what  was  previously  stored  in  the  gall  bladder,  but  also 
to  an  increased  rate  of  secretion  to  which  the  liver  is  stimulated 
by  the  same  chemical  mechanism  which  stimulates  the  flow 
of  pancreatic  juice. 

The  intestinal  juice  is  a  distinctly  alkaline  liquid  secreted  by 
the  tubular  glands  (crypts  of  Lieberkiihn)  with  which  the  small 
intestine  is  lined.     It  contains  at  least  five  enzymes :  entero- 


92  CHEMISTRY  OF  FOOD  AND  NUTRITION 

kinase,  by  the  action  of  which  trypsinogen  is  converted  into 
trypsin ,  erepsin,  which  produces  further  cleavage  of  the  pro- 
teoses and  peptones;  and  the  three  enzymes,  sucrase  (or  in- 
vertase),  maltase,  and  lactase,  which  hydrolyze  respectively  the 
three  disaccharides,  sucrose,  maltose,  and  lactose.  The  secre- 
tion of  intestinal  juice  is  probably  stimulated  by  secretin,  and 
possibly  also  by  another  hormone  whose  production  is  de- 
pendent upon  the  presence  of  pancreatic  juice. 

Careful  observations  on  the  reaction  of  the  contents  of  the 
small  intestine  were  made  by  Moore  and  Bergin  in  1897.* 
Samples  taken  through  a  fistula  immediately  above  the  ileo- 
caecal  valve  were  always  alkaline  to  methyl-orange,  lacmoid, 
and  litmus,  but  acid  to  phenolphthalein.  Hence  neither 
hydrochloric  acid,  nor  any  appreciable  amount  of  the  stronger 
organic  acids  such  as  acetic,  butyric,  or  lactic,  could  have  been 
present  in  the  free  state.  The  acid  reaction  shown  by  phe- 
nolphthalein was  probably  due  either  to  traces  of  organic  acids, 
or  possibly  to  dissolved  carbonic  acid,  or  to  acid-protein  com- 
pounds not  yet  completely  digested  and  absorbed.  It  seems 
probable  that  this  fairly  represents  the  condition  as  to  reaction 
which  exists  throughout  the  greater  part  of  the  small  intestine. 
Under  such  conditions  all  three  classes  of  foodstuffs  would  be 
readily  attacked  by  the  digestive  enzymes  present,  and  brought 
into  condition  for  absorption  —  the  carbohydrates  as  mono- 
saccharide; the  fats  as  fatty  acid  and  glycerol;  the  proteins 
(chiefly  at  least)  as  amino  acids. 

The  rate  of  passage  of  different  foodstuffs  through  the  small 
intestine  has  been  studied  by  Cannon  with  the  aid  of  the  Roent- 
gen rays,  according  to  the  general  method  already  described. 
Fat,  carbohydrate,  and  protein  foods,  uniform  in  consistency 
and  in  amount  (25  cc),  were  fed  to  cats  which  had  been  fasted 

*  Very  recently  the  subject  has  been  reinvestigated  by  Long  and  Fenger,  using 
modern  methods  for  the  actual  measurement  of  hydrogen  ion  concentration.  See 
Journal  oj  the  American  Chemical  Society,  June,  191 7. 


ENZYMES  AND   DIGESTION  93 

for  24  hours.  At  regular  intervals  for  7  hours  after  feeding, 
the  shadows  of  the  stomach  and  intestinal  contents  were  ob- 
served by  means  of  the  Roentgen  rays. 

The  process  of  rhythmic  segmentation  above  described  was 
seen  with  all  three  kinds  of  foodstuffs,  and  the  frequency  of  its 
occurrence  corresponded  roughly  to  the  amount  of  food  present 
in  the  intestine. 

Absorption  takes  place  very  readily  in  the  small  intestine  — 
more  readily  and  completely  than  can  be  explained  by  the  purely 
mechanical'  laws  of  diffusion.  On  this  account  the  process  is 
sometimes  called  "  resorption  "  to  distinguish  it  from  passive 
absorption  such  as  takes  place  by  diffusion  through  non-living 
membrane. 

Observations  have  been  made  upon  a  patient  having  a  fistula 
at  the  end  of  the  small  intestine.  In  this  case  it  was  found 
that  85  per  cent  of  the  protein  matter  of  the  food  was  absorbed 
before  this  point  was  reached,  and  the  absorption  of  the  other 
foodstuffs  is  probably  equally  complete.  For  this  patient 
the  food  began  to  pass  the  ileocaecal  valve  in  from  2  to  5^  hours 
after  eating,  but  the  time  required  from  the  eating  of  the  food 
until  the  last  portions  had  passed  into  the  large  intestine  was 
9  to  23  hours. 

Digestion  in  the  large  intestine.  —  We  have  seen  that  in 
the  small  intestine  the  conditions  are  very  favorable  both  for 
digestion  and  for  absorption,  and  that  very  much  the  greater 
part  of  the  available  nutrients  has  been  absorbed  before  the 
food  mass  reaches  the  ileocaecal  valve.  Hertz  has  observed, 
however,  that  often  the  ileum  is  still  full  at  the  end  of  four  or 
five  hours  after  the  last  trace  of  chyme  has  left  the  stomach. 
Consequently  there  may  be  an  accumulation  of  incompletely 
digested  food  and  active  digestive  enzymes  in  the  last  few  inches 
of  the  ileum,  where  it  remains  and  undergoes  digestion  for 
perhaps  a  longer  period  than  in  the  stomach.  During  all  this 
time  there  is  active  segmentation,  but  very  little  peristalsis. 


94  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Beginning  at  infrequent  intervals  some  time  after  the  chyme 
first  reaches  it,  the  ileocaecal  valve  relaxes  each  time  a  peri- 
staltic wave  passes  along  the  last  few  inches  of  the  ileum.  Can- 
non finds  that  the  ileocaecal  valve  is  physiologically  "  com- 
petent "  for  food  which  passes  through  it  normally  from  the 
small  intestine.  This  means  that  the  food  which  has  reached 
the  large  intestine  in  the  natural  way  is  ordinarily  never  forced 
back  into  the  small  intestine  again.  This  is  important  because 
in  the  anterior  portion  of  the  large  intestine  the  waves  which 
appear  most  frequently  are  those  of  antiperistalsis  —  i.e.  tend 
to  force  the  food  back  toward  the  small  intestine.  Since  the 
ileocaecal  valve  prevents  the  food  passing  oack,  these  antiperi- 
staltic waves  result  in  thoroughly  churning  the  food  in  this 
part  of  the  large  intestine  and  constantly  bringing  fresh  por- 
tions in  contact  with  the  intestinal  wall  so  that  the  conditions 
here  are  quite  favorable  for  absorption.  Moreover,  the  walls 
of  the  large  intestine  "burnish  an  alkaline  secretion  which  further 
aids  the  completion  of  the  digestive  changes  already  begun. 
So  far  as.  known  the  Targe  intestine  secretes  no  digestive  enzyme 
of  its  own. 

With  the  passage  of  material  from  the  ileum  into  the  caecum, 
the  caecum  and  ascending  colon  become  gradually  filled.  Recent 
observations  show  that  this  passive  filling  takes  place  very  slowly 
except  during  and  immediately  after  meals  (Hertz).  The 
material  remains  in  the  large  intestine  for  a  comparatively  long 
time  (generally  about  a  day,  often  longer) ;  for  the  peristaltic 
movements  which  carry  the  material  onward,  while  stronger 
than  the  waves  of  antiperistalsis,  are  of  less  frequent  occur- 
rence, at  least  in  the  first  part  of  the  large  intestine.  During 
this  time  there  is  a  marked  absorption  of  water,  along  with 
the  remaining  products  of  digestion.  The  residual  material 
gradually  beconies  more  solid  and  takes  on  the  character 
of  feces. 


ENZYMES  AND   DIGESTION  Q5 

Bacterial  Action  in  the  Digestive  Tract 

The  digestive  tract  of  an  infant  contains  no  bacteria  at  birth, 
but  usually  some  gain  access  during  the  first  day  of  Hfe.  In  the 
average  adult  it  is  estimated  that  each  day's  food  in  its  passage 
through  the  digestive  tract  is  subjected  to  the  action  of  over 
one  hundred  bilHon  bacteria,  chiefly  in  the  large  intestine. 

Since  bacteria  are  regularly  present  in  the  digestive  tract  in 
such  large  numbers,  it  has  been  questioned  whether  they  may 
not  perform  some  essential  function  in  connection  with  the  nor- 
mal processes  of  digestion.  Experiments  to  demonstrate  whether 
animals  are  independent  of  such  bacteria  are  beset  with  many 
difficulties.  Nuttall  and  Thierfelder  kept  sterile  for  several 
days  the  digestive  tracts  of  young  guinea  pigs  delivered  by 
Caesarean  section  and  fed  upon  thoroughly  steriHzed  food,  and 
as  the  animals  thus  treated  Hved  and  gained  in  weight,  the 
experimenters  concluded  that  intestinal  bacteria  are  not  es- 
sential to  normal  nutrition.  This  view  has  recently  received 
strong  support  from  the  observations  of  Levin,  who  examined 
the  intestinal  contents  of  Arctic  animals  in  Spitzenberg.  The 
digestive  tracts  of  white  bears,  seals,  reindeer,  eider  ducks,  and 
penguin  were  found  to  be  in  most  cases  free  from  bacteria, 
showing  that  the  latter  are  not  essential  to  the  normal  processes 
of  digestion  and  nutrition.  Kendall,  however,  in  citing  the  evi- 
dence presented  by  Levin,  points  out  that  Arctic  mammals, 
as  soon  as  they  are  brought  to  temperate  regions,  rapidly  ac- 
quire intestinal  bacteria  which  do  not  seem  to  interfere  with 
the  well-being  of  the  host. 

Furthermore  Schottelius  claims  that  the  conclusions  of  Nut- 
tall  and  Thierfelder  are  not  justified  since  their  experiments  did 
not  cover  a  long  enough  period.  He  himself  experimented  with 
chickens  from  bacteria-free  eggs.  One  group  kept  in  an 
absolutely  bacteria-free  environment  and  fed  on  sterile  food,  did 
well  for  ten  days,  but  thereafter  developed  very  slowly.     When 


96  CHEMISTRY  OF  FOOD  AND  NUTRITION 

they  were  given  "  infected  "  food  (containing  common  bacteria), 
they  gained  rapidly.  Meanwhile  a  second  group  which  had 
been  kept  in  a  sterile  environment  but  had  received  "  infected  " 
food  from  the  start,  grew  normally,  as  did  a  third  group  kept 
throughout  under  ordinary  conditions.  From  these  results 
SchotteHus  concluded  that  intestinal  flora  seem  to  be  necessary 
for  the  normal  development  of  chickens.  Similar  observations 
have  been  made  by  Madame  Metschinikoff  using  tadpoles, 
and  by  Moro  using  turtles. 

Notwithstanding  this  conflicting  evidence,  it  would  seem  fair 
to  conclude  from  the  observations  of  Levin  that  if  it  were 
possible  to  exclude  absolutely  all  bacteria  from  the  digestive 
tract,  the  well-being  of  the  body  would  be  in  no  wise  im- 
paired; yet  under  such  conditions  as  ordinarily  exist,  the 
bacteria  which  usually  predominate  in  the  digestive  tract  of 
the  healthy  man  probably  render  an  important  service  in 
helping  to  pro  tee  t^,;fehe 'body  against  occasional  invasions  of 
obnoxious  speciesT 

According  to  Herter,  a  few  species,  such  as  B.  lactis  aerogeneSy 
B.  coli,  B.  bifidusj  have  adapted  themselves  so  well  to  the  con- 
ditions existing  in  the  human  digestive  tract  that  they  are 
ordinarily  not  harmful  to  the  host  unless  present  in  abnormally 
large  numbers,  and  being  able  to  hold  their  own  against  new- 
comers they  may  act  beneficially  in  giving  rise  to  conditions 
which  check  the  development  of  other  types  of  organisms, 
capable  of  doing  injury,  which  under  ordinary  conditions  man 
can  hardly  prevent  from  occasionally  gaining  ingress  through 
food  or  drink. 

"  The  presence  in  the  colon  of  immense  numbers  of  obligate 
micro-organisms  of  the  B.  coli  type  may  be  an  important  de- 
fense of  the  organism  in  the  sense  that  they  hinder  the  develop- 
ment of  that  putrefactive  decomposition  which,  if  prolonged, 
is  so  injurious  to  the  organism  as  a  whole.  We  have  in  this 
adaptation  the  most  rational  explanation  of  the  meaning  of 


ENZYMES  AND  DIGESTION  97 

the  myriads  of  colon  bacilli  that  inhabit  the  large  intestine. 
This  view  is  not  inconsistent  with  the  conception  that  under 
some  conditions  the  colon  bacilH  multiply  to  such  an  extent  as 
to  prove  harmful  through  the  part  they  take  in  promoting 
fermentation  and  putrefaction." 

Proteolytic  enzymes  formed  by  intestinal  bacteria  may 
assist  in  the  digestion  of  food,  and  it  is  conceivable  that  bac- 
teria may  synthesize  proteins  or  amino  acids  which  may  then 
be  absorbed  by  the  host,  but  the  recent  experiments  of  Osborne 
and  Mendel  seem  to  show  that  this  cannot  be  an  important 
factor  in  protein  metaboHsm. 

If  for  our  present  purpose  we  consider  only  the  bacteria  which 
are  prominent  in  producing  decomposition  of  foodstuffs  in  the 
digestive  tract,  and  these  only  with  reference  to  this  one  prop- 
erty, we  may  regard  as  the  three  main  types:  (i)  the  bacteria 
of  fermentation,  such  for  example  as  the  lactic  acid  bacteria; 
(2)  the  putrefactive  bacteria,  such  as  the  anaerobic  B.  aerogenes 
capsulatus  (B.  welchii);  (3)  bacteria  of  the  B.  coli  type,  showing 
some  of  the  characters  of  both  the  fermentative  and  putre- 
factive organisms,  but  tending  in  general  to  antagonize  the 
putrefactive  anaerobes. 

Among   cases   of   excessive   bacterial   decomposition  in  the 
digestive  tract  the  fermentation  of  carbohydrates  with  pro- 
duction of  organic  acids  (and  possibly  also  alcohol)  is  most 
likely  to  occur  in  the  stomach,  while  the  putrefaction  of  pro- 
teins occurs  mainly  in  the  large  intestine.     While  it  is  true 
that  in  general  the  products  of  fermentation  tend  to  restrict 
putrefaction,  yet,  since  the  two  processes  take  place  for  the  most 
part  at  such  widely  separated  points  of  the  digestive  tract, 
there  may  be  excessive  fermentation  and  excessive  putrefac- 
I  tion  in  the  same  individual  at  the  same  time.     Among  the  con- 
I  ditions  which  favor  excessive  fermentation  are :  diminished  tone 
*  and  motiHty  of  the  stomach,  dilation,  diminution  or  absence  of 
I  free  hydrochloric  acid  in  the  gastric  juice,  and  excessive  use  of 

!  H 


98  CHEMISTRY  OF  FOOD   AND   NUTRITION 

carbohydrate  food  —  especially  sucrose  and  glucose,  which 
are  more  susceptible  to  fermentation  in  the  stomach  than  are 
lactose,  maltose  and  starch. 

In  the  normal  human  stomach  the  conditions  are  quite 
unfavorable  for  the  development  of  anaerobic  putrefactive 
bacteria,  not  only  because  of  the  presence  of  air,  but  also  because 
of  the  action  of  the  gastric  juice ;  and  favorable  conditions  are 
not  found  in  the  anterior  portion  of  the  small  intestine.  In 
the  lower  third  of  the  small  intestine  the  numbers  of  bacteria 
increase  and  among  them  sometimes  putrefactive  forms.  In 
the  large  intestine  the  conditions  are  much  more  favorable 
for  the  anaerobic  putrefactive  bacteria,  and  these  may  produce 
marked  decomposition  in  any  protein  still  remaining  unabsdrbed. 
In  general  the  greater  the  amount  of  digestible  but  undigested 
or  unabsorbed  protein  and  the  longer  the  material  stays  in  the 
large  intestine,  the  greater  the  amount  of  putrefactive  de- 
composition. Not  infrequently  excessive  fermeiltation  in  the 
stomach  causes  local  sensitiveness  which  results  in  the  taking 
of  less  bulky  food  (or  such  as  has  less  indigestible  residue), 
which  in  turn  tends  to  stagnate  in  the  intestine  and  thus  render 
the  conditions  more  favorable  for  intestinal  putrefaction.  Ac- 
cording to  Herter  there  sometimes  results  from  the  eating  of 
large  quantities  of  meat  and  sugar  a  type  of  fermentation  in 
which  oxalic  acid  is  produced  and  which  must  therefore  be 
highly  injurious;  but  ordinarily  the  products  of  fermentation 
are  only  irritating,  while  putrefaction  gives  rise  to  products 
which  are  more  distinctly  toxic.  These  include  indol,  skatol, 
phenol,  and  cresol,  which  are  for  the  most  part  absorbed  into 
the  system  and  finally  excreted  in  combination  with  sulphuric 
acid  as  "  ethereal  "  or  "  conjugated  "  sulphates.  Of  these  the 
best-known  is  potassium  indoxyl  sulphate,  commonly  called 
"  indican."  The  amounts  of  conjugated  sulphates  and  of  in- 
dican  in  the  urine  are  valuable  indications  of  the  intensity  of 
the  putrefactive  process  in  the  intestine. 


ENZYMES  AND  DIGESTION 


99 


Coeflacients  of  Digestibility  of  Food 

The  fecal  matter  passed  per  day  varies  considerably  in  health, 
but,  on  an  ordinary  mixed  diet  of  digestible  food  materials,  is 
usually  between  loo  and  200  grams  of  moist  substance  contain- 
ing 25  to  50  grams  of  solids.  The  feces  contain  any  indigestible 
substances  swallowed  with  the  food  and  any  undigested  resi- 
dues of  true  food  material;  but  ordinarily  they  appear  to  be 
largely  composed  of  residues  of  the  digestive  juices,  together 
with  certain  substances  which  have  been  formed  in  metabolism 
and  excreted  by  way  of  the  intestine,  and  bacteria,  living  and 
dead. 

Frausnitz  studied  the  feces  of  several  persons  placed  alter- 
nately on  meat  and  on  rice  diets  and  found  that,  although  the 
solids  of  the  meat  were  about  ten  times  as  rich  in  nitrogen  as 
the  solids  of  the  rice,  the  two  diets  yielded  feces  whose  solids 
were  of  practically  the  same  composition.  Some  of  the  data  of 
these  experiments  are  shown  in  the  table. 

Composition  of  Feces  from  Different  Diets  (Prausnitz) 


Person 

Principal 

FOOD 

Nitrogen  in 

DRY   FECES   PER   CENT 

Ether  Extract 

in  dry  feces 

per  cent 

Ash  in  dry 
feces  per  cent 

H.       ... 
H.       ... 
M.      .     .     . 
M.      .     .     . 
W.  P.       .     . 
W.  P.      .     . 

Rice 

Meat 

Rice 

Meat 

Rice 

Meat 

8.83 
8.75 
8.37 
9.16 

8.59 
8.48 

12.43 
15.96 
18.23 
16.04 
15.89 
17.52 

15.37 
14.74 
11.05 
12.22 
12.58 
13.13 

In  view  of  such  results  Prausnitz  considers  that  "  normal  " 
feces  have  essentially  the  same  composition  irrespective  of  the 
food,  the  quantity  of  food  residues  in  such  "  normal "  feces 
being  negligible.  From  this  point  of  view  the  feces  show  not 
so  much  the  extent  to  which  the  food  has  been  absorbed  as 


lOO  CHEMISTRY  OF  FOOD  AND  NUTRITION 

whether  it  is  a  large  or  a  small  feces-former.  On  the  other 
hand,  so  far  as  the  nitrogen  compounds  of  the  feces  are  con- 
cerned, it  is  probably  true,  as  generally  assumed,  that  they 
represent  material  either  lost  or  expended  in  the  work  of  di- 
gestion, and  therefore  that  the  nitrogen  of  the  feces  is  to  be  de- 
ducted from  that  of  the  food  in  estimating  the  amount  avail- 
able for  actual  tissue  metabolism.  This,  however,  is  by  no 
means  equally  true  of  the  ash  constituents,  many  of  which  after 
being  metabolized  in  the  body  are  eliminated  mainly  by  way  of 
the  intestine  rather  than  through  the  kidneys. 

On  a  liberal  diet  consisting  entirely  of  non-nitrogenous  food 
the  amount  of  nitrogen  in  the  feces  was  0.5  to  0.9  gram  per 
day,  which  is  more  than  is  sometimes  found  in  feces  from  food 
furnishing  enough  protein  to  meet  all  the  needs  of  the  body. 
Thus  the  expenditure  of  nitrogenous  material  in  the  digestion 
of  fats  and  carbohydrates  may  be  larger  than  in  the  digestion 
of  protein  food. 

The  feces  always  contain  fat  (or  at  least  substances  soluble 
in  ether)  as  well  as  protein.  Fasting  men  have  ehminated 
0.57  to  1.3  grams  of  "  fat "  per  day ;  and  when  the  diet  is  very 
poor  in  fat,  the  feces  may  contain  as  much  as  was  contained 
in  the  food.  As  the  fat  content  of  the  food  rises,  the  actual 
amounts  in  the  feces  increase,  but  the  relative  amounts  de- 
crease, so  that  up  to  a  certain  point  the  apparent  percentage 
utiHzation  of  the  fat  becomes  higher.  The  Hmit  to  the  amount 
of  fat  which  can  be  thus  well  digested  varies  with  the  individual 
and  with  the  form  in  which  the  fat  is  given.  Quantities  up  to 
200  grams  per  day  have  been  absorbed  to  within  2  to  3  per  cent 
when  given  in  the  form  of  milk,  cheese,  or  butter. 

In  addition  to  protein  and  fat  the  feces  always  contain  various 
other  forms  of  organic  matter  which  in  the  routine  proximate 
analyses  usually  made  in  connection  with  feeding  experiments 
are  collectively  reported  as  "  carbohydrates  determined  by 
difference." 


ENZYMES  AND  DIGESTION 


lOl 


With  these  facts  in  mind  one  may  make  use  of  the  coefficients 
of  digestibility  without  being  misled  by  them.  These  co- 
efficients show  the  relation  between  the  constituents  of  the 
food  consumed  and  the  corresponding  constituents  of  the  feces. 
Thus  if  the  feces  from  a  given  diet  contain  5  per  cent  as  much 
protein  as  was  contained  in  the  food,  this  proportion  is  as- 
sumed to  have  been  lost  or  expended  in  digestion,  and  the  co- 
efficient of  digestibihty  of  the  protein  of  the  diet  is  stated  to 
be  95  per  cent.  While  as  just  shown  this  assumption  is  not 
entirely  correct,  yet  it  is  approximately  true  of  the  organic 
nutriments  that  the  difference  between  the  amounts  in  the 
food  and  in  the  feces  represents  what  is  available  to  the  tissues 
of  the  body,  and  thus  these  coefficients  serve  a  useful  purpose 
in  the  computation  of  the  nutritive  values  of  foods. 

From  the  results  of  hundreds  of  digestion  experiments  At- 
water  computed  the  coefficients  of  digestibility  of  the  organic 
nutrients  of  the  main  groups  of  food  materials,  when  used  by 
man  as  part  of  a  mixed  diet,  to  be  as  follows :  — 

Average  Coefficients  of  Digestibility  of  Foods  when  Used  in  Mixed 
Diet  (Atwater) 


Protein 

Fat 

Carbohydrates 

PER   CENT 

PER   CENT 

PER   CENT 

Animal  foods 

97 

95 

98 

Cereals  and  breadstuJBfs 

85 

90 

98 

Dried  legumes      .... 

78 

90 

97 

Vegetables 

83 

90 

95 

Fruits 

85 

90 

90 

Total  food  of  average  mixed 

diet 

92 

95 

98 

In  some  cases  these  figures  are  higher  than  have  been  re- 
ported for  similar  foods  by  other  observers,  the  differences 
being  due  mainly  to  the  fact  (not  formerly  recognized)  that  a 
food  may  be  more  perfectly  utiHzed  when  fed  as  part  of  a 


102  'CHE:\ilST&^  'OF'  FPOD  AND   NUTRITION 

simple 'mixed' diet  than  wKeri  fed  alone.  Milk  is  an  example 
of  such  a  food,  and  has  when  consumed  as  part  of  a  mixed  diet 
a  much  higher  coefficient  of  digestibility  than  is  often  assigned 
to  it  on  the  basis  of  earUer  experiments. 

It  will  be  seen  that  the  coefficients  differ  less  for  the  different 
types  of  food  than  might  be  expected  from  popular  impressions 
of  "  digestibihty "  and  "  indigestibiUty."  It  is  also  note- 
w^orthy  that  the  coefficients  of  digestibility  are  less  influenced 
by  the  conditions  under  which  the  food  is  eaten  and  vary  less 
with  individuals  than  is  generally  supposed.  In  explanation 
of  this  it  may  be  noted  that  general  impressions  of  digestibility 
relate  mainly  to  ease  of  digestion  and  particularly  to  ease  and 
rapidity  of  gastric  digestion,  and  that  there  is  little  direct 
relation  between  the  ease  with  which  a  food  is  digested  in  the 
stomach  and  the  extent  to  which  it  is  ultimately  digested  in 
its  passage  through  the  entire  digestive  tract.  Substances 
which  are  resistant  to  gastric  digestion  will  tend  to  remain  long 
in  the  stomach  and  will  probably  excite  a  greater  flow  of  gastric 
juice.  Thus  a  greater  amount  of  acid  chyme  will  enter  the 
duodenum,  and  this  will  result  in  the  secretion  of  a  greater 
amount  of  pancreatic  juice  also. 

Similarly  an  increase  in  the  amount  of  food  eaten  may  have 
little  effect  upon  the  coefficient  of  digestibility  of  the  foodstuffs. 
In  a  series  of  experiments  by  the  writer  it  was  found  that  the 
doubling  of  a  small  diet  decreased  the  coefficient  of  digestibility 
by  less  than  i  per  cent.  Snyder  reports  that  as  between  medium 
and  large  amounts  of  oatmeal  and  milk,  the  protein  was  7  per 
cent  and  the  fat  6  per  cent  more  completely  absorbed  in  the 
case  of  the  medium  ration. 

REFERENCES 

Bayliss.     Principles  of  General  Physiology. 
Bayliss.     The  Nature  of  Enzyme  Action. 
Cannon.    The  Mechanical  Factors  of  Digestion. 


ENZYMES  AND  DIGESTION  IO3 

Cannon  and  Washburn.  An  Explanation  of  Hunger.  American  Journal 
of  Physiology,  Vol.  29,  page  441  (191 1). 

Carlson.    The  Control  of  Hunger  in  Health  and  Disease. 

Effront.     Les  Catalyseurs  Biochemique. 

EuLER.     General  Chemistry  of  the  Enzymes. 

Falk  and  Sigiura.  The  Esterase  and  Lipase  of  Castor  Beans.  Journal 
of  the  American  Chemical  Society,  Vol.  37,  page  217  (1915). 

Falk.  An  Experimental  Study  of  Lipolytic  Actions.  Proceedings  of 
National  Academy  of  Science,  Vol.  i,  page  136  (March  1915).  Journal 
of  Biological  Chemistry,  Vol.  31,  page  97  (1917). 

Fischer.     Physiology  of  Alimentation. 

Hull  and  Keeton.  The  Existence  of  a  Gastric  Lipase.  Journal  of  Bio- 
logical Chemistry,  Vol.  32,  page  127  (191 7). 

Herter.     Bacterial  Infections  of  the  Digestive  Tract. 

Howell.    Textbook  of  Physiology. 

Mathews.    Physiological  Chemistry,  Chapters  8,  9,  10. 

Metchnikoff  and  Woolman.  Studies  on  Intestinal  Putrefaction.  An- 
nates de  VInstitute  Pasteur,  Vol.  27,  page  825  (1912). 

Nelson  and  Vosburgh.  Kinetics  of  Invertase  Action.  Journal  of  the 
American  Chemical  Society,  Vol.  39,  page  790  (April  191 7). 

Oppenheimer.    Die  Fermente. 

Osborne.  The  Chemical  Nature  of  Diastase.  Journal  of  the  American 
Chemical  Society,  Vol.  17,  page  593  (1895).    ' 

Osborne  and  Mendel.  The  Contribution  of  Bacteria  to  the  Feces.  Jour- 
nal of  Biological  Chemistry,  Vol.  18,  page  177  (1914). 

Pawlow.    The  Work  of  the  Digestive  Glands. 

ScHMmT  and  Strassburger.  Die  Faezes  des  Menschen  in  normalen  und 
krankhaften  Zustande. 

Sherman  and  Gettler.  The  Forms  of  Nitrogen  in  Pancreatic  and  Malt 
Amylase  Preparations.  Journal  of  the  American  Chemical  Society, 
Vol.  35,  page  179  (1913). 

Sherman  and  Schlesinger.  Pancreatic  Amylase.  Ihid.,  Vol.  33,  page 
1195;  Vol.  34,  page  1104;  Vol.  37,  page  1305  (1911-1915). 

Starling.    Recent  Advances  in  the  Physiology  of  Digestion. 

Taylor.    Digestion  and  Metabolism. 

Vernon.    Intracellular  Enzymes. 


CHAPTER  V 
THE   FATE    OF   THE    FOODSTUFFS    IN    METABOLISM 

CARBOHYDRATES 

The  carbohydrate  of  the  food,  having  been  converted  into 
monosaccharides  in  the  intestine,  is  taken  up  by  the  capillary 
blood  vessels  of  the  intestinal  wall  and  passes  from  them  into 
the  portal  vein.  After  a  meal  rich  in  carbohydrate  the  blood 
of  the  portal  vein  is  rich  in  glucose,  sometimes  reaching  twice 
its  normal  glucose  content ;  and  may  show  levulose  and  galac- 
tose as  well.  In  the  blood  of  the  general  circulation,  however, 
only  glucose  is  found,  and  this  remains  small  in  quantity  — 
about  one  tenth  of  one  per  cent  —  even  after  a  meal  rich  in 
carbohydrates,  so  that  a  considerable  part  of  the  carbohydrate 
taken  must  be  stored  temporarily  in  the  liver  and  given  up 
gradually  to  the  blood  in  the  form  of  glucose,  thus  keeping  nearly 
constant  the  glucose  content  of  the  blood  of  the  general  cir- 
culation. The  carbohydrate  thus  stored  in  the  liver  cells  is 
deposited  in  the  form  of  glycogen,  which,  after  an  abundant 
meal,  may  reach  lo  per  cent  of  the  weight  of  the  liver  (or,  in 
rare  cases,  an  even  higher  figure)  and  may  fall  to  nearly  nothing 
when  no  carbohydrate  food  has  been  taken  for  some  time. 
To  a  less  extent  the  muscles  store  glycogen  in  a  similar 
way,  their  glycogen  contents  var3dng  from  traces  to  about  2 
per  cent. 

The  fact  that  the  carbohydrate  stored  in  the  liver  after  a 
meal  is  so  largely  converted  into  glucoar^nd  passes  into  the 

104 


THE   FATE  OF  THE  FOODSTUFFS  IN  METABOLISM       105 

blood  current  before  the  next  meal,  while  the  glucose  content 
of  the  blood  remains  small  and  nearly  constant,  indicates  that 
the  glucose  of  the  blood  must  be  quite  rapidly  used,  and  from 
ourLpreserLL.standpoiiitthe  most  important  question  of  the  car- 
b^iydrate  jnetabohsin_jsl:he  tate  of  the  glucose  carried  to  the 


muscles  and  other  tissues  by  the  blood. 


Oxidation  of  Carbohydrate 

By  comparison  of  the  arterial  and  venous  blood,  it  is  plain 
that  in  its  passage  through  the  muscles  the  blood  becomes 
poorer  in  glucose  and  oxygen  and  richer  in  carbon  dioxide,  and 
this  change  is  more  marked  when  the  muscle  is  active  than 
when  it  is  at  rest.  The  oxidation  of  glucose  in  the  muscles  is 
in  some  way  dependent  upon  the  pancreas,  but  the  exact  func- 
tion of  the  pancreas  .in  this  connection  is  still  obscure.  It  is 
not  to  be  supposed  that  the  glucose  is  burned  directly  to  carbon 
dioxide  and  water.  There  is  much  evidence  that  the  glucose 
molecule  is  broken  before  oxidation,  and  in  all  probability  this 
first  cleavage  yields  mainly  three-carbon  compounds. 

Some  lactic  acid  is  always  produced  by  working  muscle  and 
this  has  long  been  regarded  as  a  possible  intermediate  product 
in  the  metaboHsm  of  glucose.*  Lactic  acid  appears  to  bear 
important  relationships  both  to  carbohydrate  metabolism  and 
to  muscle  contraction.  The  discussion  of  the  significance  and 
role  of  lactic  acid  cannot  be  attempted  here.  It  may  be  said, 
however,  that  in  recent  years  much  experimental  evidence  has 
accumulated  in  support  of  the  view  that  lactic  acid  is  not 
formed  directly  from  glucose,  but  rather  through  the  interven- 
tion of  other  three-carbon  compounds,  probably  glyceric  alde- 
hyde or  methyl  glyoxal  (pyruvic  aldehyde)  or  both. 

*  It  should  perhaps  be  noted  here  that  lactic  acid  plays  a  part  not  only  in  the 
metabolism  of  carbohydrate  but  of  other  foodstuffs  as  well.  It  may  be  formed, 
for  instance,  from  glycerol  and  from  certain  amino  acids. 


lo6  CHEMISTRY  OF  FOOD  AND   NUTRITION 

If  we  think  of  the  glucose  molecule  as  first  breaking  into 
three-carbon  molecules  with  a  minimum  of  internal  rearrange- 
ment, the  most  probable  primary  product  would  appear  to  be 
glyceric  aldehyde,  the  formation  of  which  might  be  represented 
crudely  as  follows : 

CH2OH  •  CHOH  •  CHOi  H  •  CHOH  •  CHOH  •  CHO 

Or,  to  write  the  reaction  in  a  more  usual  form, 

CeHiaOe  ->-  2  CH2OH  •  CHOH  •  CHO 

Glucose  Glyceric  aldehyde 

It  is  also  possible  that  the  first  product  of  cleavage  of  glu- 
cose may  be  pyruvic  aldehyde  or  methyl  glyoxal : 

CeHiaOe-^  2  CH3  •  CO  •  CHO  +  2H2O 

Glucose  Methyl  glyoxal 

(Pyruvic  aldehyde) 

Both  glyceric  aldehyde  and  methyl  glyoxal  have  been  shown 
to  result  from  the  cleavage  of  glucose  under  the  influence  of 
alkaU  in  vitro  and  there  are  doubtless  enzymes  in  the  tissues 
which  catalyze  one  or  both  of  these  reactions  with  the  result 
that  glucose  readily  undergoes  such  cleavage  as  a  preliminary 
to  oxidation  in  the  body. 

Opinion  is  at  present  divided  as  to  whether  glyceric  aldehyde 
or  pyruvic  aldehyde  (methyl  glyoxal)  is  to  be  regarded  as  the 
usual  first  step  in  glucose  metabolism.  In  either  case  it  is  prob- 
able that  the  bulk  of  the  carbohydrate  material  passes  through 
the  form  of  pyruvic  aldehyde  (methyl  glyoxal)  on  its  way  to 
oxidation. 

According  as  we  assume  the  process  to  go  on  with  or  with- 
out the  intermediary  formation  of  glyceric  aldehyde,  the  pro- 
duction of  lactic  acid  from  glucose  in  the  body  may  be  rep- 
resented in  either  of  the  following  ways : 

CeHizOe^  CH2OH  •  CHOH  •  CHO-^  CH3  •  CO  •  CHO 

Glucose  Glyceric  aldehyde  Pyruvic  aldehyde 


THE  FATE  OF  THE  FOODSTUFFS   IN  METABOLISM      107 

->  CH3  •  CHOH  .  COOH 

Lactic  acid 

or 

CeHiaOe^  CH3  •  CO  •  CHO-^  CH3CHOH  •  COOH 

Glucose  Pyruvic  aldehyde  Lactic  acid 

Each  of  these  reactions  has  been  brought  about  in  the  labora- 
tory by  heating  with  alkah  and  at  the  lower  alkaHnity  of  the 
body  the  tissue  enzymes  are  believed  to  catalyze  the  same  or 
similar  changes.  Moreover  it  has  been  shown  that  under  suit- 
able experimental  conditions  lactic  acid  is  formed  from  gly- 
ceric aldehyde  and  from  pyruvic  aldehyde  by  the  action  of 
surviving  liver  tissue ;  and  the  further  fact  that  in  experimental 
diabetes  glucose  may  be  formed  from  glyceric  or  pyruvic  alde- 
hyde as  well  as  from  lactic  acid  tends  also  to  confirm  the  behef 
that  these  aldehydes  are  intermediary  products  between  glucose 
and  lactic  acid  —  both  in  normal  metabolism  and  experimental 
diabetes.  Glycerol  also  when  perfused  through  liver  tissue  yields 
lactic  acid,  and  since  the  first  product  of  oxidation  of  glycerol  is 
in  all  probability  glyceric  aldehyde,  we  have  here  a  further  reason 
for  beheving  that  the  latter  is  a  normal  precursor  of  lactic  acid. 
There  has  been  no  direct  demonstration  of  the  presence  of 
glyceric  aldehyde  or  of  pyruvic  aldehyde  (methyl  glyoxal)  in 
the  body ;  but  this  is  probably  due  to  their  unstable  or  highly 
reactive  nature.  The  view  that  glyceric  aldehyde  passes  through 
pyruvic  aldehyde  in  being  transformed  into  lactic  acid  is  not 
only  probable  on  stereochemical  grounds  but  is  strongly  sup- 
ported by  much  recent  evidence  indicating  that  pyruvic 
aldehyde  occupies  a  central  position  in  the  intermediary  me- 
tabolism. 

Thus  far  in  our  study  of  the  catabolism  of  glucose  we  have 
considered  no  oxidative  changes  but  only  the  cleavages  and 
transformations  which,  from  the  standpoint  of  the  use  of  glu- 
cose as  fuel,  may  be  regarded  as  preHminary  to  oxidation. 
Probably  the  first  oxidation  product  to  be  formed  in  glucose 


lo8  CHEMISTRY  OF  FOOD  AND  NUTRITION 

catabolism  is  pyruvic  acid,  CH3  •  CO  •  COOH.  This  may  be 
formed  by  the  oxidation  either  of  pyruvic  aldehyde  or  of  lactic 
acid.  The  relation  of  the  three  substances  may  be  represented 
thus: 

CH3  •  CO  •  CHO I^  CH3  •  CHOH  •  COOH 

Pyruvic  aldehyde  Lactic  acid 

X  A" 

CH3  •  CO  •  COOH 

Pyruvic  acid 

Pyruvic  aldehyde  and  lactic  acid  are,  so  to  speak,  upon  the 
same  energy  plane.  Molecule  for  molecule  they  are  of  equal 
fuel  value  and  either  is  readily  convertible  into  the  other.  The 
conversion  of  pyruvic  acid  into  lactic  acid  or  pyruvic  aldehyde 
probably  takes  place  under  certain  conditions,  but  this  involves 
reduction  and  so  is  not  to  be  expected  in  the  normal  course  of 
glucose  oxidation.  The  fate  of  pyruvic  acid  under  normal  con- 
ditions is  probably  to  undergo  further  oxidation  through  acetic 
acid  to  carbonic  acid  and  water.  It  is  possible  that  acetalde- 
hyde  or  alcohol  or  both  may  intervene  between  pyruvic  acid 
and  acetic  acid,  and  that  formic  acid  may  be  produced  as  an 
intermediate  step  between  acetic  and  carbonic  acids. 

To  summarize  what  now  appears  to  be  the  most  promising 
theory  of  the  intermediary  metaboHsm  of  carbohydrate,  we 
may  say  that  the  glucose  is  first  transformed,  either  directly  or 
through  glyceric  aldehyde,  into  PYmvic  aldehyde  (methyl 
glyoxal),  which  may  either  be  changed  to  lactic  acid  or  oxidized 
directly  to  pyruvic  acid  that  readily  undergoes  oxidation  to 
carbon  dioxide  and  water  through  steps  not  yet  fully  worked 
out.  Lactic  acid  may  also  be  converted  into  pyruvic  acid  and 
thus  ultimately  be  completely  oxidized.  In  case  of  excessive 
formation  or  inadequate  oxidation,  as  in  extreme  muscular 
fatigue  or  asphyxial  conditions,  lactic  acid  may  accumulate 
in  the  body  or  may  be  excreted  unchanged. 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      1 09 
Glucose 

Glyceric  aldehyde  $  Methyl  glyoxal  :|^  Lactic  acid 

\  / 

Pyruvic  acid 

\ 
(Acetic  aldehyde) 

(Acetic  acid) 

\ 

(Formic  acid?) 

Carbonic  acid 

Whatever  the  exact  mechanism  of  the  process,  a  large  part 
of  the  glucose  brought  by  the  blood  is  oxidized  in  the  muscles 
to  furnish  energy,  which  appears  as  external  or  internal  work. 

In  general,  the  rate  at  which  combustion  takes  place  in  the 
tissues  depends  upon  the  activity  of  the  tissue  cells,  rather  than 
upon  the  supply  either  of  combustible  matter  or  of  oxygen. 
When  a  sufficient  supply  of  oxygen  is  provided,  any  further 
increase  has  little  effect  upon  the  rate  of  combustion,  and,  as 
we  have  seen,  any  excess  of  carbohydrate  instead  of  being  burned 
is  stored  as  glycogen.  But  while  the  absorption  of  an  abun- 
dance of  carbohydrate  does  not  greatly  change  the  amount  of 
combustion  taking  place  in  the  body,  it  may  result  in  the  use 
of  carbohydrate  as  fuel  almost  to  the  exclusion  of  fat  for  the 
time  being,  as  is  shown  by  observations  upon  the  respiratory 
quotient. 

The  respiratory  quotient  is  the  quotient  obtained  by  di- 
viding the  volume  of  carbon  dioxide  given  off  in  respiration  by 
the  volume  of  oxygen  consumed.     That  is  — 

Volume  of   CO.  produced  ^  .,  r      5,^^       quotient." 
Volume  of  O2  consumed 


110  CHEMISTRY  OF  FOOD  AND  NUTRITION 

The  numerical  value  of  this  quotient  will  evidently  depend 
upon  the  elementary  composition  of  the  materials  burned.  Car- 
bohydrates will  yield  a  quotient  of  i.o  since  they  contain  hy- 
drogen and  oxygen  in  proportions  to  form  water,  so  that  all 
oxygen  used  to  burn  carbohydrate  goes  to  the  making  of  carbon 
dioxide,  and  each  molecule  of  O2  so  consumed  will  yield  one 
molecule  of  CO2,  occupying  (under  the  same  conditions  of 
temperature  and  pressure)  the  same  amount  of  space  as  the 
oxygen  consumed  to  produce  it.  Thus  in  burning  a  molecule 
of  glucose,  six  molecules  of  oxygen  are  consumed  and  six  mole- 
cules of  carbon  dioxide  produced : 

CeHiaOe  +  6  O2  -^  6  CO2  +  6  H2O. 

Here  the  volumes  of  oxygen  and  of  carbon  dioxide  are  equal 
and  the  respiratory  quotient  is  i.o. 

Fats  contain  much  more  hydrogen  than  can  be  oxidized  by 
the  oxygen  present  in  the  molecule,  and  therefore  a  part  of  the 
oxygen  used  to  burn  fat  goes  to  form  water,  so  that  the  volume 
of  oxygen  consumed  is  greater  than  the  volume  of  carbon  di- 
oxide produced,  which  gives  a  respiratory  quotient  lower  than 
I.o.  The  common  fats  of  the  body  and  of  the  food  give  quo- 
tients approximating  0.7.  Thus  the  oxidation  of  stearin  is 
represented  by  the  equation: 

2C57H110O6  +  16302-^  114  CO2  +  110H2O. 

Since  163  volumes  of  oxygen  are  consumed  and  114  volumes 
of  carbon  dioxide  produced,  the  respiratory  quotient  is 

114         ^ 
163 

Proteins  give  quotients  intermediate  between  those  of  car- 
bohydrates and  fats,  but  if  the  amount  of  protein  used  in  the 
body  be  determined  by  other  methods  (see  Chapter  VIII) 
and  allowed  for,  one  may  then  deduce  from  the  respiratory 
quotient  the  proportions  of  carbohydrates  and  fats  which  are 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      III 

being  burned  in  the  body  at  any  given  time.  The  body  will 
show  a  respiratory  quotient  of  i.o  when  burning  carbohydrate 
alone,  of  0.7  when  burning  fat  alone,  and  of  an  intermediate 
value  when  both  fat  and  carbohydrate  are  being  burned.  If, 
now,  the  respiratory  quotient  rises  soon  after  the  eating  of 
carbohydrate  food,  it  is  evident  that  the  carbohydrate  is  being 
used  more  freely  and  fat  less  freely  than  before. 

In  an  experiment  by  Magnus-Levy  the  subject  before  taking 
food  showed  a  quotient  of  0.77.  He  then  ate  155  grams  of  cane 
sugar,  after  which  the  quotient  was  determined  at  intervals  of 
an  hour  for  7  hours  with  the  following  results:  i.oi,  0.89, 
0.89,  0.92,  0.82,  0.82,  0.79.  The  quotient  here  shows  that 
within  an  hour  after  the  sugar  was  eaten  the  body  was  making 
use  of  the  carbohydrate  to  such  an  extent  that  fat  either  was 
not  being  used  at  all  or  was  being  formed  from  carbohydrate 
as  fast  as  it  was  burned;  and  that  for  seven  hours  after  the 
meal  the  body  continued  to  use  carbohydrate  to  a  greater,  and 
fat  to  a  less,  extent  than  was  the  case  at  the  beginning  of  the 
experiment. 

It  has  been  pointed  out  that,  when  carbohydrate  is  absorbed 
in  larger  quantity  than  is  required  to  meet  the  body's  immediate 
needs  for  fuel,  the  surplus  normally  accumulates  as  glycogen, 
which  is  stored  conspicuously  in  the  liver,  but  also  to  a  con- 
siderable extent  in  the  muscles  and  other  organs.  The  amount 
of  carbohydrate  which  will  be  stored  in  the  entire  body  after 
rest  and  hberal  feeding  is  estimated  at  300  to  400  grams.  Thus 
the  total  amount  of  carbohydrate  which  can  be  stored  as  such 
in  the  body  is  no  more  than  is  frequently  taken  in  one  day's 
food. 

When  the  supply  of  carbohydrate  is  so  abundant  that  it 
continues  in  excess  of  the  needs  of  the  body  and  accumulates 
until  the  liver  and  muscles  have  no  tendency  to  increase  their 
store  of  glycogen,  the  further  surplus  of  carbohydrate  tends 
to  be  converted  into  fat. 


112  CHEMISTRY  OF  FOOD  AND  NUTRITION 


Production  of  Fat  from  Carbohydrate 

Experimental  evidence  of  the  transformation  of  carbohydrate 
into  fat  has  been  cited  in  Chapter  II  where  it  was  shown  that 
animals  which  fatten  readily  on  carbohydrate  food  may  store 
more  body  fat  than  could  possibly  be  derived  from  the  fats 
and  proteins  eaten ;  that  milch  cows  have  yielded  more  fat  in 
the  milk  than  could  be  accounted  for  on  any  other  assumption 
than  that  fat  was  formed  from  carbohydrate;  and  that  there 
may  be  more  carbon  stored  in  the  body  from  the  carbohydrate 
food  eaten  by  a  fattening  animal  than  can  be  accounted  for 
in  any  other  way  than  that  a  part  of  the  carbon  taken  into  the 
body  as  carbohydrate  was  retained  as  body  fat. 

Further  proof  of  the  ability  of  the  animal  body  to  change 
carbohydrate  into  fat  is  obtained  from  the  respiratory  quotient. 
As  noted  above,  observations  made  after  a  fast  tend  to  show 
quotients  approaching  that  of  fat,  while  after  feeding  carbohy- 
drates the  quotient  may  rise  rapidly.  If  the  quotient  reaches 
i.o,  it  shows  that  the  body  as  a  whole  is  using  carbohydrate 
and  not  fat  as  fuel;  and  a  quotient  greater  than  i.o  may  be 
taken  as  evidence  that  the  carbohydrate  is  itself  supplying  part 
of  the  oxygen  which  appears  as  carbon  dioxide,  or,  in  other 
words,  that  it  is  breaking  down  in  such  a  way  that  a  part  is 
burned  while  another  part  goes  to  form  in  the  body  a  substance 
more  highly  carbonaceous  and  having  a  lower  respiratory 
quotient  than  the  carbohydrate  itself.  In  many  cases  it  is 
certain  that  this  substance  can  be  nothing  but  fat.  Respiratory 
quotients  greater  than  i.o  have  been  observed  after  liberal 
carbohydrate  feeding  in  several  species,  including  man.  Each 
such  observation  furnishes  evidence  of  a  conversion  of  car- 
bohydrate into  fat. 

The  formation  of  fat  from  carbohydrate  in  the  animal  body 
is  therefore  estabhshed  by  four  distinct  lines  of  experimental 
evidence:   (i)  by  determination  of  the  amounts  of  body  fat 


THE  FATE  OF  THE  FOODSTUFFS  IN   METABOLISM      II3 

formed,  (2)  by  determination  of  the  milk  fat  produced,  (3)  by 
observation  of  the  amount  of  carbon  stored,  (4)  by  observations 
upon  the  respiratory  quotient. 

Chemical  Steps  in  the  Formation  of  Fat  from  Carbohydrate 

While  there  is  no  doubt  whatever  of  the  abiHty  of  the  animal 
to  synthesize  fat  from  carbohydrate,  the  mechanism  of  the  pro- 
cess is  far  from  clear.  As  expressed  by  Leathes,  *'  the  chemical 
changes  involved  are  fascinating  in  their  obscurity."  What- 
ever the  exact  steps,  the  transformation  of  carbohydrate  into 
fatty  acid  radicles  must  involve  reduction  of  hydroxyl  groups 
and  condensations  to  form  the  long  chains  of  the  higher  fatty 
acids.  We  have  already  seen  that  in  what  we  believe  to  be  the 
normal  course  of  carbohydrate  catabohsm  there  occurs,  either 
along  #ith  or  quickly  following  the  breaking  of  the  glucose 
molecule  into  three-carbon  compounds,  a  reduction  of  certain 
hydroxyl  groups  with  transfer  of  the  oxygen  so  that  substances 

jSud^s  methyl  glyoxal,  pyruvic  acid,  and  lactic  acid  are  formed. 

^WlPpyruvic  acid  or  lactic  acid  acetaldehyde  may  be  formed ; 
two  molecules  of  acetaldehyde  may  then  undergo  aldol  conden- 
sation and  the  aldol  be  transformed  (by  simultaneous  reduction 
and  oxidation,  or  transfer  of  oxygen  from  the  P  to  the  terminal 
carbon)  into  butyric  ^cid.  Such  an  hypothesis  is  consistent 
with  reactions  observed  in  vitro  and  with  the  well-known  pro- 
duction of  butyric  acid  in  certain  bacterial  fermentations  of 
sugar  and  of  lactic  acid.  Leathes  favors  this  hypothesis  and 
comments  upon  it  (in  part)  as  follows :  "  The  biochemical  sig- 
nificance of  the  synthesis  of  butyric  acid  from  lactic  acid  and 
from  sugar  by  bacteria  becomes  greater,  however,  when  it  is 
remembered  that  in  this  fermentation  normal  caproic  acid  is 
simultaneously  formed,  and  as  Raper  showed  also,  though  in 
still  smaller  amount,  normal  octoic  or  capryHc  acid.  ...  In 
butyric  fermentation  it  seems  that  the  reactions  that  lead  to 
the  synthesis  of  butyric  acid  may  lead  to  the  synthesis  of  acids 


114  CHEMISTRY  OF  FOOD  AND  NUTRITION 

of  longer  chains  but  still  unbranched  and  containing  an  even 
number  of  carbon  atoms,  in  other  words,  that  these  acids  may 
be  produced  by  condensation  of  two,  three,  or  four  acetic  alde- 
hyde molecules.  In  higher  organisms,  plants  or  animals,  this 
same  condensation  carried  further  would  result  as  Nencki  sug- 
gested in  the  formation  of  the  series  of  acids  with  straight  chains 
of  even  numbers  of  carbon  atoms  leading  up  to  palmitic  and 
stearic  acid."  Raper^  has  shown  experimentally  that  con- 
densation of  two  molecules  of  aldol  in  alkaline  solution  yields  a 
straight  chain  product  which  on  oxidation  and  reduction  by 
laboratory  methods  yields  normal  octoic  (caprylic)  acid. 

Smedley  has  developed  an  alternative  hypothesis  regarding 
the  mechanism  of  fatty  acid  synthesis  from  carbohydrate 
material. 

According  to  Smedley ,2  the  most  probable  starting  point  is 
pyruvic  acid. 

As  an  intermediary  step  in  the  metabolism  of  carbohydrate, 
pyruvic  acid  is  probably  formed  in  large  quantities  in  the 
body,  though  its  reactivity  may  prevent  it  from  accumulating 
in  measurable  amounts. 

Pyruvic  acid  readily  breaks  down  to  acetaldehyde  and 
carbon  dioxide.  It  also  condenses  with  aldehydes  to  form  prod- 
ucts which,  under  conditions  similar  to  those  existing  in  the 
body,  undergo  rearrangements  (through  simultaneous  or  suc- 
cessive oxidation  and  reduction)  which  result  in  the  spHtting 
out  of  carbon  dioxide  leaving  an  acid  of  two  more  carbon  atoms 
than  were  contained  in  the  original  aldehyde;  or  an  aldehyde 
of  two  more  carbon  atoms  than  the  original  aldehyde  may  be 
formed,  and  this  in  turn  react  with  another  molecule  of  pyruvic 
acid  forming  a  fatty  acid  or  aldehyde  of  two  more  carbon  atoms. 

Each  of  these  hypotheses  assumes  as  a  starting  point  only 

1  /.  Chem.  Soc,  Vol.  91,  page  1831  (1907).  See  also  Leathes,  The  Fats,  pages 
106-109. 

^Journal  of  Physiology,  Vol.  45,  Proc.  page  26;  Biochemical  Journal,  Vol.  7, 
page  364. 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      II 5 

substances  which  we  have  good  reason  to  believe  are  regularly 
formed  in  carbohydrate  metabolism,  and  both  are  consistent 
with  the  well-known  fact  that  natural  fats  contain  fatty  acid 
radicles  having  all  multiples  of  two  carbon  atoms  from  four 
to  eighteen,  but  none  containing  uneven  numbers  of  carbon 
atoms  in  the  molecule. 

FAT 

In  digestion  the  fat  is  split  into  fatty  acids  and  glycerol 
which,  however,  upon  absorption  are  recombined  into  neutral 
fat.  It  is  beheved  that  this  recombination  occurs  during  the 
passage  of  these  digestion  products  through  the  intestinal 
wall.  The  fat  thus  absorbed  is  taken  up  by  the  lymph  vessels 
rather  than  the  capillary  blood  vessels,  and  is  poured  with  the 
lymph  into  the  blood.  The  fat  which  renders  the  blood  plasma 
turbid  at  the  height  of  absorption  will  usually  have  passed  from 
the  blood  into  the  tissues  after  a  few  hours.  The  fat  thus 
leaving  the  blood  may  be  burned  as  fuel,  or  stored  for  use  as 
fuel  in  the  future,  and  a  part  may  be  transformed  into  tissue 
lipoid  or  enter  into  combination  with  proteins  to  form  some  of  the 
chemically  more  complex  substances  of  cellular  protoplasm,  cell 
membrane,  or  of  the  central  nervous  system.  The  fat  burned 
as  fuel  serves  as  a  source  of  energy  for  muscular  work  and  other 
activities  essentially  as  does  carbohydrate.  The  average  re- 
sults of  a  very  complete  series  of  experiments  by  Atwater  and 
his  associates  indicated  that  the  potential  energy  of  fat  was 
95.5  per  cent  as  efficient  as  that  of  carbohydrates  for  the  pro- 
duction of  muscular  work. 

Oxidation  of  Fat 

The  glycerol  from  fat  is  presumably  oxidized  to  glyceric  alde- 
hyde which  passes  to  methyl  glyoxal,  whose  fate  is  doubtless 
the  same  in  this  case  as  when  the  same  substance  is  formed  in 
carbohydrate  metabolism. 


Il6  CHEMISTRY  OF  FOOD  AND  NUTRITION 

The  fatty  acid  presents  a  separate  problem.  Through  the 
work  of  Dakin,  and  of  Knoop  and  Embden  the  "  beta-oxidation 
theory  "  has  been  developed  and  is  now  generally  accepted.  Ac- 
cording to  this  theory  the  fatty  acid  is  attacked  by  oxidation  at  the 
/8-carbon  atom  with  the  probable  formation  first  of  )8-hydroxy, 
and  then  of  /8-ke tonic  acids.  Further  oxidation  at  this  point  must 
then  cause  a  separation  of  the  a-  and  )8-carbon  atoms ;  thus  two 
carbons  of  the  original  fatty  acid  break  away,  presuniably  to  un- 
dergo complete  oxidation,  and  there  remains  a  fatty  acid  with  two 
less  carbon  atoms  than  the  original.  By  such  a  process  stearic 
acid  would  yield  palmitic ;  palmitic  would  yield  myristic ;  myris- 
tic,  lauric ;  and  so  on  to  butyric  acid.  Beta-oxidation  of  butyric 
acid  would  yield  successively  /8-oxybutyric,  and  acetoacetic  acid. 
Normally  the  acetoacetic  acid  should  yield  two  molecules  of 
acetic,  which  in  turn  should  burn  to  carbon  dioxide  and  water. 

The  sequence  of  changes  from  caproic  acid  to  the  final  oxida- 
tion products  would  thus  be  as  follows : 

Caproic     ^-oxy        /3-keto     Butyric    /3-oxy       Aceto-     Acetic     Carbonic 

ACID  (hydroxy)  caproic  BUTYRIC     ACETIC 

CH3      ->CH3      ->CH3      ->CH3      ->CH3     ->CH3     ->2CH3  ->4C02 

I         I         I         I         I        I        I 

CH2  CH2  CH2  CH2  CHOH    CO2         COOH    +4H2O 

I  I  I  I  I  I 

CH2  CH2  CH2  CH2  CH2         CH2 

CH2  CHOH     CO  COOH     COOH    COOH 

III 
CH2  CH2  CH2 

I  I  I 

COOH      COOH      COOH 

When  the  normal  process  is  interfered  with  or  overtaxed,  an- 
other reaction  may  occur  with  the  formation  from  acetoacetic 
acid  of  carbon  dioxide  and  acetone,  which  latter  like  acetoacetic 
acid  and  /Jroxybutyric  acid  sometimes  appears  in  the  urine, 
especially  in  many  cases  of  diabetes  meUitus.  The  acidosis  of 
diabetes  is  believed  to  be  due  to  the  )8-oxybutyric  acid  and 
acetoacetic  acid  thus  formed.    Acetone,  acetoacetic  acid,  and 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      1 17 

/8-oxybutyric  acid  are  sometimes  spoken  of  collectively  as  "  ace- 
tone bodies."  For  further  discussion  of  the  intermediary  metab- 
olism of  fat  and  of  the  evidence  that  the  acidosis  of  diabetes 
is  chiefly  due  to  acids  arising  from  fat  metabolism,  the  reader 
is  referred  to  Dakin's  Oxidations  and  Reductions  in  the  Animal 
Body  and  the  chapter  on  diabetes  in  Lusk's  Science  of  Nutrition. 

Storage  of  Food  Fat  in  the  Body 

That  fat  derived  from  the  food  may  be  stored  as  body  fat 
has  already  been  shown  (Chapter  III)  and  need  not  be  dis- 
cussed further  here.  Recently  Mills  ^  has  found  that  fatty 
oils  injected  with  antiseptic  precautions  into  the  subcutaneous 
tissue  may  under  favorable  conditions  be  absorbed  therefrom 
and  used  in  the  body  in  the  same  way  as  if  obtained  by  feeding. 
Whether  fat  once  deposited  in  the  tissues  will  remain  and  ac- 
cumulate, or  be  returned  to  the  circulation  and  used  as  fuel, 
will  depend  upon  the  balance  between  the  food  consumption 
and  the  food  requirements  of  the  organism  as  a  whole.  In  this 
respect,  there  is  no  difference  between  fat  consumed  and  de- 
posited as  such  and  fat  formed  in  the  body  from  other  food 
materials. 

Can  Carbohydrate  be  Formed  from  Fat? 

Glycerol  is  readily  convertible  into  glucose  in  the  body, 
probably  passing  through  the  form  of  glyceric  aldehyde  as  an 
intermediate  step;  but  the  glycerol  radicle  represents  only 
about  one  twentieth  of  the  energy  value  of  the  fat  molecule. 

Whether  carbohydrate  is  ever  fdb»ed  from  fatty  acid  in  the 
animal  body  is  an  open  question. 

As  evidence  of  such  formation  of  carbohydrate  from  fat, 
Hill  cites  observations  upon  hibernating  animals  showing  in- 
crease of  glycogen  during  sleep,  accompanied  by  respiratory 
quotients  lower  than  0.7. 

^Archives  of  Internal  Medicine,  Vol.  7,  page  694  (191 1). 


Il8  CHEMISTRY  OF  FOOD   AND   NUTRITION 

On  the  other  hand,  in  phlorizin  poisoning  *  and  severe  diabetes 
when  it  would  seem  that  all  material  in  the  body  capable  of 
transformation  into  glucose  is  being  thus  changed,  there  does 
not  appear  to  be  a  production  of  glucose  from  fat  (fatty  acid). 
As  this  latter  type  of  experimentation  has  been  extensively  em- 
ployed while  relatively  little  evidence  of  the  sort  cited  by  Hill 
has  been  presented,  the  trend  of  opinion  is  rather  away  from  the 
view  that  the  animal  body  can  form  carbohydrate  from  fatty 
acid  radicles,  or  transform  fat  into  carbohydrate  beyond  the 
limited  amount  obtainable  from  the  glyceryl  radicles  of  the 
fat.  It  has  been  suggested  that  the  low  respiratory  quotients 
above  mentioned  may  be  due  to  accidental  fluctuations,  since 
the  blood  does  not  always  show  the  same  carbon  dioxide  con- 
tent. The  question  of  actual  transformation  of  fat  into  car- 
bohydrate is  not  of  great  practical  importance  in  normal  nu- 
trition, because  under  normal  conditions  fats  may  be  used 
interchangeably  with  carbohydrates  as  source  of  energy  to  a 
very  large,  though  not  unlimited,  extent. 

PROTEINS 

It  is  now  believed  that  the  hydrolysis  of  proteins  to  amino 
acids  in  the  digestive  tract  is  practically  complete.  The  sig- 
nificance of  this  digestive  cleavage  Hes  not  simply  in  the  for- 
mation of  more  soluble  and  more  readily  diffusible  substances, 
but  also  in  the  resolution  of  the  complex  molecules  of  food 
protein  into  their  simple  amino  acid  "  building  stones  "  ("  Bau- 
steine  ")  which  may  be  rearranged  by  the  body  in  the  synthesis 
of  its  own  tissue  proteins. 

*  Phlorizin  causes  very  great  glycosuria  and,  if  the  poisoning  is  continued,  the 
usual  symptoms  of  severe  diabetes  such  as  muscular  weakness,  acidosis,  acetonuria, 
and  death  in  coma.  From  moderate  dosage,  however,  the  animal  recovers.  The 
glucose  content  of  the  blood  falls  (instead  of  rising  as  in  true  diabetes) .  The  action 
of  the  phlorizin  appears  to  be  primarily  upon  the  kidneys,  causing  them  to  secrete 
glucose  much  more  rapidly  than  usual,  thus  draining  off  the  glucose  from  the  blood 
and  keeping  it  below  the  normal  level. 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      119 

Absorption  and  Distribution  of  Protein  Digestion  Products 

The  work  of  the  past  few  years,  to  be  described  in  the  para- 
graphs which  follow,  indicates  that  the  amino  acids,  resulting 
from  digestive  hydrolysis  of  the  food  proteins,  pass  through  the 
intestinal  wall  and  into  the  blood  of  the  portal  vein  unchanged, 
are  carried  through  the  Hver  into  the  blood  of  the  general  cir- 
culation and  are  thus  distributed  throughout  the  body,  and  are 
rapidly  absorbed  from  the  blood  into  the  various  tissues.  Thus 
each  tissue  receives  its  protein  material  in  the  form  of  amino 
acids  from  which  can  be  synthesized  the  particular  kind  of 
protein  characteristic  of  the  tissue  in  question.  In  other  words, 
each  tissue  makes  its  own  proteins  from  the  amino  acids  brought 
by  the  blood.  Amino  acids  not  used  in  synthesizing  protein 
(whether  brought  by  the  blood  or  formed  by  breakdown  of 
tissue  material)  are  broken  down  or  deaminized  in  the  tissues 
in  the  manner  described  beyond. 

A  brief  account  of  recent  work  on  the  distribution  and  im- 
mediate fate  of  the  amino  acids  may  serve  to  give  a  more  ade- 
quate impression  of  the  modern  view. 

In  1906  Howell  obtained  a  qualitative  reaction  for  amino  acids 
in  the  blood,  but  conclusive  evidence  of  the  relation  of  these 
amino  acids  to  metabolism  required  the  development  of  better 
methods  than  were  then  available  for  the  estimation  of  amino  acid 
nitrogen  in  the  fluids  and  tissues  of  the  body.  Such  methods  were 
developed  and  applied  independently  and  almost  simultaneously 
in  191 2  by  Folin  and  Denis  and  by  Van  Slyke  and  Meyer. 

Folin  and  Denis  distinguished  between  the  nitrogen  of  pro- 
teins, non-proteins,  ammonia,  and  urea.  The  non-protein 
nitrogen  includes  that  of  amino  acids  and  they  were  able  to 
show  that  this  form  of  nitrogen  increased  in  the  blood  and 
tissues  when  glycine  or  a  mixture  of  amino  acids  resulting 
from  pancreatic  digestion  of  protein  was  undergoing  absorption 
from  the  small  intestine.     Moreover  the  increase  in  the  non- 


120  CHEMISTRY  OF  FOOD  AND  NUTRITION 

protein  nitrogen  of  the  blood  and  muscles  was  nearly  sufficient 
to  account  for  the  nitrogenous  material  absorbed  from  the 
intestine,  from  which  it  appeared  that  they  had  traced  the  ab- 
sorbed amino  acids  and  found  them  to  be  carried  through  the 
blood  and  to  the  muscles  without  being  either  built  up  into 
protein  or  broken  down  into  ammonia  or  urea  on  the  way. 
Urea  formation  was  found  to  follow  distinctly  later  than  the 
absorption  and  distribution  of  the  amino  acids. 

Van  Slyke  and  Meyer  estimated  amino  acids  by  quantita- 
tive determination  of  the  nitrogen  present  as  amino  groups  in 
the  non-protein  fraction  of  the  blood  or  tissue.  They  found 
that,  during  the  digestion  of  protein,  amino  acids  pass  through 
the  intestinal  wall  and  appear  not  only  in  the  portal  blood  but 
also  in  the  blood  of  the  general  circulation,  showing  that  the 
amino  acids,  for  the  most  part  at  least,  pass  both  the  intestinal 
wall  and  the  liver  unchanged. 

Closely  following  the  work  of  Folin  and  of  Van  Slyke,  Rona 
(191 2)  demonstrated  by  experiments  upon  isolated  segments  of 
intestine  that  the  amino  acids  pass  unchanged  through  the 
intestinal  wall;  Abel  (1913)  dialyzed  free  amino  acids  from  the 
circulating  blood  of  living  animals  by  means  of  his  vivi-diffusion 
apparatus  and  actually  separated  alanine  in  crystalline  form; 
and  Abderhalden  (1914)  separated  glycine,  alanine,  vaHne, 
leucine,  aspartic  acid,  glutamic  acid,  lysine,  arginine,  histidine, 
and  tryptophane  from  large  quantities  of  shed  blood.  Soon 
afterward  (191 5)  Henriques  and  Andersen  showed  that  dogs 
and  goats  could  be  kept  in  a  normal  condition  of  nutrition  and 
might  even  store  nitrogen  and  gain  weight  when  they  were 
nourished  exclusively  by  intravenous  injection  of  a  food  solution 
containing  nitrogen  only  in  the  form  of  completely  digested 
protein  —  a  strong  confirmation  both  of  the  completeness  of 
cleavage  of  protein  in  normal  digestion  and  of  the  fact  that  the 
body  is  nourished  by  free  amino  acids  carried  by  the  blood  with- 
out intervention  of  chemical  changes  in  the  intestinal  wall. 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      121 

Van  Slyke  (working  upon  dogs)  continued  his  investigation 
of  the  fate  of  the  amino  acids  and  found  that  they  are  rapidly 
taken  up  from  the  blood  by  the  tissues  where  they  seem  to  be 
held  by  adsorption.  Since  the  amino  acids  can  be  extracted 
by  means  of  cold  water  or  alcohol  they  do  not  seem  to  be  held 
in  chemical  combination  with  the  tissue  proteins  nor  can  simple 
diffusion  account  for  the  extent  to  which  they  enter  the  tissues, 
because  they  rapidly  attain  a  higher  concentration  in  the  muscle 
and  Hver  cells  than  in  the  blood  with  which  these  are  in  contact. 
The  extent  to  which  this  concentration  of  amino  acids  in  the 
muscles  may  go  seems  to  have  a  fairly  definite  Hmit  at  about 
75  milligrams  of  amino  acid  nitrogen  per  loo  grams  of  muscle. 
In  the  case  of  liver  tissue  this  "  saturation  capacity  "  seems 
somewhat  more  elastic  and  the  concentration  may  reach  about 
twice  the  maximum  observed  in  muscle,  i.e.  up  to  150  milli- 
grams of  amino  acid  nitrogen  per  100  grams  of  liver.  In  the 
muscles  the  amino  acids  taken  up  as  just  described  disappear 
only  very  gradually  and  may  not  seem  to  be  appreciably 
changed  for  several  hours ;  in  the  liver  they  disappear  rapidly ; 
in  the  kidney,  pancreas,  and  spleen  they  disappear  less  rapidly 
than  in  the  liver. 

The  disappearance  of  the  amino  acids  from  the  tissues  may 
be  due  either  to  a  building  up  into  protein  or  a  breaking  down 
with  the  formation  of  ammonia  and  urea  or  both.  It  seems 
probable  that  in  general  both  processes  go  on  in  all  tissues, 
each  tissue  building  its  own  proteins  and  each  also  taking  part 
In  the  deaminization  of  amino  acids  with  formation  of  am- 
monia or  urea.  The  more  rapid  disappearance  of  amino  acids 
from  the  Hver  tissue  is  probably  due  to  the  greater  activity  of 
the  liver  in  deaminization  and  urea  formation,  especially  since 
Van  Slyke  has  recently  measured  the  increase  of  urea  in  the 
blood  on  its  passage  through  the  hver  and  shown  that  the 
passage  of  the  blood  through  the  muscle  under  parallel  con- 
ditions does  not  increase  its  urea  content  to  a  measurable  extent. 


122  CHEMISTRY  OF  FOOD  AND   NUTRITION 

Van  Slyke's  experiments  also  show  that  the  blood  contains 
amino  acids  at  all  times  and  that  the  tissues  are  not  freed  from 
amino  acids  by  fasting,  while  on  the  other  hand  high  protein 
feeding  does  not  result  in  any  great  accumulation  of  amino 
acids  as  such  either  in  the  blood  or  tissues.  All  these  observa- 
tions confirm  the  view  that  amino  acids  are  the  normal  inter- 
mediary products  in  both  the  building  up  and  breaking  down  of 
body  protein  and  that  any  large  storage  of  nitrogen  in  the  body 
must  be  due  to  formation  of  body  protein  and  not  to  mere  ac- 
cumulation of  free  amino  acids. 

Utilization  of  Protein  in  the  Tissues 

The  proteins  of  the  digested  food,  absorbed  and  distributed 
in  the  form  of  amino  acids  as  described  above,  soon  become 
available  for  nutrition ;  and  among  other  functions  they,  like 
the  carbohydrates  and  fats,  may  be  burned  *  as  fuel  for  muscular 
work.  Pfluger  proved  that  protein  may  serve  as  a  source  of 
muscular  energy  by  feeding  a  dog  for  7  months  exclusively  upon 
meat  practically  free  from  fat  and  carbohydrate,  and  requiring 
it  throughout  the  experiment  to  do  considerable  amounts  of 
work,  the  energy  for  which  must  in  this  particular  case  have 
been  derived  largely  from  the  protein  consumed. 

The  experimental  facts  and  theoretical  explanations  regard- 
ing the  breaking  down  of  proteins  (or  of  the  amino  acids  arising 
from  them)  in  the  body  tissues  must  now  be  considered.  By 
experiment  it  has  been  found  that  if  a  meal  extra  rich  in  pro  4 
tein  be  eaten,  an  increased  eUmination  of  nitrogenous  end  pro- 
ducts can  be  observed  within  2  or  3  hours,  and  probably  much 
the  greater  part  of  the  surplus  nitrogen  will  have  been  excreted 
within  24  hours  of  the  time  it  was  taken  into  the  stomach.  It 
does  not  follow,  however,  that  the  whole  of  the  protein  mole- 

*  It  will  of  course  be  understood  that  the  protein  is  not  supposed  to  be  burned 
directly.  Protein  is  split  to  amino  acids,  the  amino  acids  deaminized,  and  the  non- 
nitrogenous  residues  of  the  amino  acids  are  burned. 


THE   FATE  OF  THE   FOODSTUFFS  IN  METABOLISM       123 

cule  is  broken  down  and  eliminated  so  quickly,  and  many  ex- 
periments have  shown  that  the  carbon  often  does  not  leave  the 
body  so  rapidly  as  does  the  nitrogen.  Evidently,  the  nitrog- 
enous radicles  of  the  protein  may  be  split  off  in  such  a  way  as 
to  leave  a  non-nitrogenous  residue  in  the  body,  and  the  study  of 
protein  metabolism  involves  a  consideration  of  the  fate  of 
both  the  nitrogenous  and  the  non-nitrogenous  derivatives. 
The  fate  of  the  latter  may  conveniently  be  considered  first 
on  account  of  its  relation  to  the  metaboHsm  of  carbohydrates 
and  fats.  Of  special  interest  is  the  problem  to  what  extent  the 
deaminized  cleavage  products  of  protein  may  be  actually  trans- 
formed into  carbohydrate  or  fat  in  the  body. 

Formation  of  Carbohydrate  from  Protein 

As  early  as  1876  Wolffberg  tested  the  formation  of  carbohy- 
drate from  protein  by  fasting  fowls  for  two  days  in  order  to 
free  them  from  glycogen  and  then  feeding  for  two  days  with 
meat  powder  which  had  been  washed  free  from  carbohydrate. 
Two  of  the  fowls  were  killed  soon  after  this  protein  feeding 
and  showed  more  glycogen  in  their  livers  and  muscles  than  could 
be  accounted  for  except  as  derived  from  the  protein  fed.  Two 
similar  fowls  killed  17  and  24  hours  after  feeding  showed  much 
less  glycogen.  This  formation  of  glycogen  from  protein  was 
fully  confirmed  by  Kulz  in  a  long  series  of  experiments  in  which 
the  food  consisted  of  chopped  meat  thoroughly  extracted  with 
warm  water  (Lusk). 

Independent  evidence  of  the  production  of  carbohydrates 
from  protein  is  found  in  the  work  of  Seegen,  who  chopped  and 
mixed  the  liver  of  a  freshly  killed  animal  and  determined  the 
amount  of  carbohydrate  in  it  by  analysis  of  a  portion,  while 
the  remainder  was  kept  at  body  temperature  and  sampled  for 
analysis  from  time  to  time.  The  percentage  of  carbohydrate 
was  found  to  increase,  showing  that  the  liver  cells  can  form  car- 
bohydrate from  their  own  protein  substance. 


124.  CHEMISTRY- OF  FOOD  AND   NUTRITION 

The  most  striking  evidence  of  the  origin  of  carbohydrate  from 
protein  in  the  animal  body  is  found  in  the  many  observations 
and  experiments  which  have  been  made  in  cases  of  diabetes, 
and  in  experimental  glycosuria  produced  either  by  administra- 
tion of  phlorizin  or  by  removal  of  the  pancreas.  In  such  cases 
large  amounts  of  carbohydrate  may  be  given  off  in  the  form  of 
glucose  even  when  there  is  Httle  body  fat  and  no  carbohydrate 
or  fat  is  fed.  The  glucose  must  therefore  result  from  the  me- 
tabolism of  protein.  In  Lusk's  exhaustive  experiments  upon 
dogs  rendered  diabetic  by  phlorizin,  58  per  cent  of  the  total 
weight  of  protein  broken  down  in  the  body  (whether  in 
fasting  or  on  a  meat  diet)  was  eliminated  in  the  form  of 
glucose.  According  to  Lusk :  "  After  ingestion  of  protein  in 
the  normal  organism  this  sugar  becomes  early  available  and 
may  be  burned  before  the  nitrogen  belonging  to  it  is  ehmi- 
nated,  or,  if  the  sugar  be  formed  in  excess,  it  may  be  stored 
as  glycogen  in  the  liver  and  muscles  for  subsequent  use.  In 
this  way  it  is  obvious  that  at  least  half  the  energy  in  protein 
may  be  independent  of  the  curve  of  nitrogen  elimination,  but 
may  rather  act  as  though  it  had  been  ingested  in  the  form  of 
carbohydrates." 

The  way  in  which  the  production  of  carbohydrate  from  pro- 
tein may  take  place  has  received  much  attention.  Lusk  dem- 
onstrated experimentally  that  alanine,  one  of  the  cleavage  prod- 
ucts of  all  known  proteins,  may  yield  glucose  abundantly  in 
the  body ;  and  he  suggested  that  the  change  might  occur  through 
the  formation  of  lactic  acid  as  an  intermediary  product,  since 
he  had  already  shown  that  lactic  acid  is  convertible  into  glu- 
cose. The  work  of  Dakin  has  thrown  further  light  on  the 
intermediate  steps  of  this  transformation.  He  has  shown  that 
glyoxals  have  been  formed  from  a-amino  and  a-hydroxy  acids, 
in  vitro  —  e.g.  pyruvic  aldehyde  (methyl  glyoxal)  from  alanine 
and  lactic  acid ;  and  on  the  other  hand  a-hydroxy  acids  have 
been  formed  from  glyoxals,  both  in  vivo  and  in  vitro. 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      12$ 
•      CH3— CHNH2— COOH  ->-  CH3— CO— CHO  +  NH3 

Alanine  Methyl  glyoxal 

CH3— CHOH— COOH  t  CH3— CO— CHO  +  H2O 

Lactic  acid  Methyl  glyoxal 

Attempts,  however,  to  synthesize  amino  acids  directly  from 
glyoxals  in  vitro  were  not  successfuL  There  is  some  evidence 
of  that  synthesis  in  vivo,  but  it  cannot  be  considered  as  fully 
estabHshed  whether  it  takes  place  directly  by  the  addition  of 
ammonia  to  free  glyoxals,  or  whether  the  a-amino  acid  is  formed 
secondarily  from  the  a-ketonic  acid,  resulting  from  the  oxidation 
of  glyoxals.  The  work  of  Knoop  and  of  Embden  and  Schmitz 
leaves  no  doubt  of  the  abihty  of  the  liver  cells  to  form  amino 
acids  from  the  ammonium  salts  of  the  corresponding  a-ketonic 
acids.  Alanine,  phenylalanine,  and  tyrosine  were  produced  in 
this  way.*  It  is  of  course  possible  that  there  may  have  occurred, 
in  these  Hver  perfusion  experiments,  intermediate  steps  not 
recognized  by  the  investigators,  but  this  does  not  detract  from 
the  significance  of  the  fact  that  the  synthesis  of  amino  acids 
from  ammonium  salts  has  now  been  repeatedly  demonstrated 
by  experiment. 

The  relations  emphasized  by  Dakin  may  be  represented  as 
follows : 

Glucose  Protein 

(Glyceric  aldehyde  ?)  (Amino  acids  including) 

II  II 

Lactic  acid  ^  Methyl  glyoxal  IS^    Alanine 

■Pyruvic  acid^'^ 

to  further  oxidation 

*  Embden  also  obtained  alanine  after  perfusion  of  ammonium  lactate,  but  the 
lactate  may  have  been  first  changed  to  pyruvate  and  the  alanine  formed  from  the 
latter. 


126  CHEMISTRY  OF  FOOD  AND   NUTRITION 

Attention  may  be  called  in  passing  to  the  possible  importance 
of  the  interrelations  of  alanine,  methyl  glyoxal,  and  lactic 
acid  to  the  regulation  of  neutrality,  not  only  in  the  body  as  a 
whole  (Chapter  IX)  but  also  in  the  particular  cells  in  which 
deamination  may  be  more  active  than  oxidation.  It  will  be 
noted  that  alanine  (a  nearly  neutral  substance)  yields  on  de- 
amination another  neutral  substance  (methyl  glyoxal)  and  a 
base  (ammonia) 

CH3— CHNH2— COOH-^  CH3— CO— CHO  +  NH3 

And  furthermore  that  the  neutral  substance  methyl  glyoxal 
may  react  with  water  to  form  lactic  acid 

CH3— CO— CHO  +  H2O  ->-  CH3— CHOH— COOH 

Experiments  in  vitro  have  shown  that  the  production  of 
lactic  acid  from  methyl  glyoxal  is  promptly  checked  unless  the 
free  acid  is  quickly  neutrahzed;  also  that  the  conversion  of 
alanine  into  methyl  glyoxal  and  ammonia  is  accelerated  by  acids 
(Dakin). 

Thus  far  the  possible  mechanism  of  formation  of  carbohydrate 
from  protein  cleavage  products  has  been  considered  here  chiefly 
in  terms  of  alanine.  To  what  extent  is  its  behavior  representa- 
tive of  that  of  the  other  amino  acids?  Experiments  in  vitro 
show  that  the  transformation  of  an  a-amino  acid  into  the  cor- 
responding a-ketonic  aldehyde  is  a  very  general  reaction.  Dakin 
and  Dudley  demonstrated  it  for  all  the  amino  acids  with  which 
they  worked  —  glycine,  alanine,  phenylalanine,  vaUne,  leucine, 
and  aspartic  acid.  Experiments  in  vivo  (chiefly  on  dogs  ren- 
dered diabetic  by  phlorizin  poisoning)  have  shown  that  glycine, 
alanine,  serine,  cystine,  aspartic  acid,  glutamic  acid,  arginine, 
and  proline  are  all  capable  of  yielding  large  amounts  of  glu- 
cose. Leucine,  tyrosine,  and  phenylalanine  when  similarly 
administered  to  phlorizinized  dogs  increase  the  eHmination  of 
acetoacetic    acid    rather   than   glucose.      Valine,   lysine,   and 


THE   FATE  OF  THE  FOODSTUFFS  IN  METABOLISM       127 

tryptophane  yield  neither  glucose  nor  acetoacetic  acid  to  any 
important  extent  (Dakin). 

The  amino  acids  which  yield  glucose  are  called  glucogenetic, 
and  the  amount  of  glucose  which  a  given  protein  can  yield  in 
the  body  will  naturally  depend  upon  the  glucogenetic  amino 
acid  radicles  which  it  contains.  Since  the  amino  acids  result- 
ing from  protein  hydrolysis  cannot  be  quantitatively  recovered 
by  any  laboratory  method  thus  far  developed,  it  is  not  yet 
possible  to  calculate  just  how  much  carbohydrate  a  given  protein 
should  theoretically  yield.  For  meat  protein  and  some  others 
the  yield  has  been  determined  experimentally  as  in  Lusk's  in- 
vestigations cited  above.  For  further  discussion  of  this  point 
see  Lusk's  Science  of  Nutrition. 

We  have  therefore  abundant  evidence  from  the  work  of  in- 
dependent investigators,  using  different  methods,  that  the 
animal  body  may  form  carbohydrates  readily  and  in  large  pro- 
portion from  the  protein  of  the  food;  and  the  mechanism  of 
the  process  is  beginning  to  be  fairly  well  understood. 

Production  of  Fat  from  Protein 

There  has  been  much  controversy  regarding  the  formation 
of  fat  from  protein  in  the  animal  body.  A  number  of  observa- 
tions by  Voit  which  were  believed  to  demonstrate  such  a  pro- 
duction of  fat  were  subjected  to  vigorous  criticism  by  Pfiiiger 
and  apparently  shown  to  be  capable  of  other  interpretations. 
Later  experiments  by  Cremer  in  Voit's  laboratory  appear, 
however,  to  establish  the  formation  of  body  fat  from  protein 
food  beyond  reasonable  doubt. 

Thus  in  one  of  these  experiments  a  cat  after  a  preliminary 
period  of  fasting  was  placed  in  a  respiration  apparatus  and 
fed  Hberally  with  lean  meat  for  eight  days.  The  amount  of 
protein  broken  down  in  the  body  was  estimated  from  the  nitro- 
gen eUminated.    The  carbon  eliminated  was  also  measured, 


128  CHEMISTRY  OF  FOOD  AND  NUTRITION 

and  it  was  found  that  58.4  grams  of  carbon  had  been  retained 
in  the  body.  This  would  correspond  to  130  grams  of  glycogen, 
but  the  total  amount  of  glycogen  in  the  body  at  the  end  of  the 
experiment  was  only  35  grams,  hence  about  three  fourths  of 
the  carbon  retained  by  the  cat  from  the  protein  food  must 
have  been  stored  as  body  fat. 

The  evidence  of  formation  of  milk  fat  in  part  from  protein, 
while  perhaps  not  amounting  to  a  mathematical  demonstration, 
is  still  very  strong. 

Since  there  is  already  abundant  experimental  evidence  of  the 
production  of  carbohydrate  from  protein  and  of  the  transfor- 
mation of  carbohydrate  into  fat,  it  is  evident  that  protein  food 
can  indirectly,  if  not  directly,  contribute  to  the  formation  of 
fat  in  the  body. 

The  Fate  of  the  Nitrogen  in  Protein  Metabolism 

It  has  already  been  shown  that  the  nitrogen  of  the  protein 
of  food  enters  the  circulation  chiefly,  if  not  wholly,  as  amino  acids 
and  is  taken  up  as  amino  acids  by  the  various  body  tissues. 
The  amino  acids  thus  obtained  by  the  tissues  from  the  food 
serve  as  material  for  the  building  up  of  body  proteins ;  but  in 
the  breaking  down  of  body  proteins  there  is  doubtless  a  Uber- 
ation  of  amino  acids  of  the  same  kinds.  Amino  acids  from 
either  source  are  subject  to  deaminization  in  the  tissues,  and  in 
so  far  as  a-amino  groups  are  concerned  the  process  doubtless 
consists  chiefly  in  the  splitting  out  of  the  nitrogen  as  ammonia, 
most  of  which  is  later  changed  to  urea.  Nitrogen  in  other 
forms  than  a-amino  acids  may  be  expected  to  undergo  a  some- 
what different  metabolism,  and  it  is  well  known  that  the  urine 
always  contains  other  nitrogen  compounds  in  addition  to 
ammonium  salts  and  urea. 

Much  light  has  been  thrown  upon  the  chemistry  of  protein 
metabolism  by  the  study  of  the  quantitative  relations  existing 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      1 29 

among  the  different  forms  of  nitrogen  in  the  urine  under  dif- 
ferent conditions.  For  our  present  purpose  it  will  be  sufficient 
to  consider  only  the  more  important  of  the  nitrogen  compounds 
of  the  urine  and  the  relations  which  they  are  believed  to  bear 
to  the  processes  of  normal  metabolism. 

Urea.  —  The  proteins,  on  being  metabolized  in  the  body, 
yield  varying  amounts  of  arginine,  which  may  undergo  hydroly- 
sis into  ornithine  and  urea.  In  this  way  a  small  part  of  the 
nitrogen  of  protein  may  reach  the  urea  stage  through  a  series 
of  direct  cleavages.  It  is  altogether  probable,  however,  that 
much  the  greater  part  of  the  urea  eliminated  arises  as  follows : 
The  protein  in  catabolism  is  split  to  amino  acids,  which  are 
deaminized  (as  in  the  conversion  of  alanine  to  methyl  glyoxal 
above  mentioned),  the  nitrogen  of  the  amino  group  being  split 
out  as  ammonia,  which  with  the  carbonic  acid  constantly  being 
produced  in  metaboHsm  forms  ammonium  carbonate.*  Loss 
of  one  molecule  of  water  yields  ammonium  carbamate,  which 
in  turn  on  loss  of  one  molecule  of  water  yields  urea. 

(NH4)2C03  -V  NH4CO2NH2  +  H2O 

NH4C02NH2^  CO(NH2)2  +  H2O 

Ammonium  chloride  or  sulphate  evidently  cannot  be  changed 
to  urea  in  this  way ;  and  experiments  show  that  if  hydrochloric 
or  sulphuric  acid  is  introduced  into  the  blood,  it  is  eliminated 
by  the  kidneys  largely  as  ammonium  salt,  and  the  quantity  of 
urea  is  correspondingly  decreased.  In  diseased  conditions  of 
the  liver  the  organic  salts  of  ammonia  (which  normally  should 
be  burned  to  carbonate  and  then  converted  as  above)  may  also 
pass  through  and  be  eliminated  without  being  changed  to  urea. 
In  health  and  on  a  full  protein  diet  (say  about  100  grams  protein 
per  day)  from  82  to  %%  per  cent  of  the  total  nitrogen  excreted 
by  the  kidneys  is  usually  in  the  form  of  urea.  On  a  low  protein 
diet  this  percentage  is  lower. 

*  If  ammonium  salts  of  organic  acids  are  first  formed,  the  complete  oxidation 
of  the  organic  acid  radicle  will  bring  this  ammonia  also  into  the  form  of  carbonate. 
K 


130  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Ammonia.  —  As  already  noted,  ammonia  is  evidently  a 
normal  precursor  of  urea,  being  changed  to  the  latter  in  part 
in  the  muscles  and  other  tissues  generally  and  in  part  during 
its  passage  through  the  liver.  In  accordance  with  this  view 
we  find  that  the  elimination  of  nitrogen  as  ammonia  may  be 
notably  increased  at  the  expense  of  urea:  (i)  in  structural  dis- 
eases of  the  liver;  (2)  after  injecting  mineral  acids  which 
combine  with  ammonia  in  the  body,  forming  stable  ammonium 
salts ;  (3)  in  cases  of  a  pathological  excess  of  acids  in  metabolism, 
such  as  often  occurs  in  diabetes  and  in  fevers.  All  of  these  are, 
of  course,  abnormal  conditions.  Normally,  about  2  to  6  per  cent 
of  the  total  nitrogen  eliminated  is  in  the  form  of  ammonium 
salts,  the  amount  depending  largely  upon  the  relation  between 
the  amounts  of  acid-forming  and  of  base-forming  elements  in 
the  food,  which  will  be  discussed  in  connection  with  the  study 
of  the  ash  constituents  of  food  and  of  .mineral  metaboHsm 
(Chapter  X). 

Uric  acid  and  the  purine  bases  (nucleic  acid  metabolism). — 
A  part  of  the  nitrogen  of  human  urine  is  always  in  the  form  of 
uric  acid  and  purine  bases.  These  owe  their  origin  either  to 
the  free  purine  substances  of  the  food,  such  as  the  guanine  and 
hypoxanthine  of  meat  extract,  or  to  the  metabolism  of  nucleic 
acid  derived  from  the  nucleoprote\ns  of  the  food  or  of  the  body 
tissues.  The  constituent  groups  of  the  nucleic  acids  and  the 
order  of  their  hberation  on  hydrolytic  cleavage  such  as  occurs 
in  metabolism  may  be  represented  by  the  following  diagram 
adapted  from  the  works  of  Wells  and  of  Jones : 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      131 
Nucleoprotein 

Protein  Nuclein 


Protein  Nucleic  acid  {NtLcleotide) 

Phosphoric  acid  Nucleoside 


Carbohydrate 

f  Purine  bases 
Adenine 
Guanine 
Base<!  Pyrimidine  bases 
Cytosine 
Thymine 
Uracil 

Explanation  of  diagram.  —  The  distinction  between  nucleo- 
proteins  and  nucleins  is  somewhat  arbitrary  and  perhaps  of 
doubtful  value.  Wells  regards  nucleoproteins  simply  as  com- 
plexes containing  a  larger  proportion  of  protein  than  is  con- 
tained in  nucleins  or  vice  versa.  Jones  prefers  to  discuss  nuclein 
metabolism  entirely  in  terms  of  nucleic  acid  in  order  to  avoid 
the  danger  of  unnecessary  confusion  with  protein  metabolism. 
The  nucleic  acids  do  not  contain  any  radicles  found  in  simple 
proteins ;  they  are  compounds  of  phosphoric  acid  and  carbohy- 
drate with  purine  and  pyrimidine  bases  in  which  the  acid  and 
base  radicles  are  not  linked  to  each  other  but  both  to  the  car- 
bohydrate radicle.  Phosphoric  acid-carbohydrate-base  chains 
of  this  sorFare  called  nucleotides,  and  the  nucleic  acids  contain- 
ing four  such  chains  in  the  molecule  are,  in  this  terminology, 
tetranucleotides.  Nucleotidases  are  enzymes  which  split  nucleic 
acids  Hberating  the  phosphoric  acid  and  leaving  compounds  of 
carbohydrate  with  base  which  are  collectively  known  as  nucleo- 


132  CHEMISTRY  OF  FOOD  AND   NUTRITION 

sides.  Nucleosidases  are  enzymes  splitting  nucleosides  into 
their  constituent  carbohydrates  and  bases.  In  the  case  of  plant 
nucleic  acid  the  carbohydrate  is  a  pentose  ((i.ribose)  and  the 
bases  are  adenine,  guanine,  cytosine,  and  uracil.  In  animal 
nucleic  acid  the  carbohydrate  is  that  of  a  hexose  and  the  bases 
are  adenine,  guanine,  cytosine,  and  thymine. 

Lusk  summarizes  the  hydrolysis  of  yeast  nucleotides  as 
follows : 

Nmleotide — H3PO4  ■>•  Nucleoside — (/.ribose  -^  Base 
Adenylic  acid  ->-  Adenosine  -»-  Adenine 

Guanyhc  acid  ->-  Guanosine  ->■  Guanine 

Cytodin-nucleotide     ->-  Cytodine  ->■  Cytosine 

Uridin-nucleotide        ->-  Uridine  ->•  Uracil 

And  to  show  at  a  glance  the  characteristic  cleavage  products 
of  the  two  types  of  nucleic  acid : 

Animal  nucleic  acid  Plant  nucleic  acid 

(Thymus)  (Yeast) 

Phosphoric  acid Phosphoric  acid 

Guanine Guanine 

Adenine Adenine 

Cytosine Cytosine 

Thymine Uracil 

Hexose Pentose 

Formulce  and  relationships.  —  The  chemical  relationships 
of  the  purine  bases  and  uric  acid  so  far  as  these  are  shown  by 
empirical  formulae  are  as  follows : 

Purine,  C5H4N4 

Adenine,  C5H3N4NH2,  amino-purine 
Guanine,  C5H3N4ONH2,  amino-oxy-purine 
Hypoxanthine,  C5H4N4O,  oxy-purine 
Xanthine,  C5H4N4O2,  dioxy-purine 
Uric  acid,  C5H4N4O3,  trioxy-purine 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      133 

Uric  acid,  the  most  highly  oxidized  of  these  purines,  is  the 
one  chiefly  found  in  the  urine. 

The  chemical  relations  of  these  substances  to  each  other  are 
more  fully  shown  by  the  structural  formulae  given  on  this  page. 

The  chemical  structure  of  the  pyrimidine  bases  is  indicated 
by  the  following  formulae : 


Cytosine 

N=    C— NH2 

I  I 

CO     CH 

I         II 
NH— CH 


Thymine 

NH— CO 

I  I 

CO    C— CH3 

I     II 

NH— CH 


Uracil 

NH— CO 

I  I 

CO     CH 

I  II 

NH— CH 


6-amino,  2-oxy-pyrimidine     s-methyl,  2, 6-dioxy-pyrimidine     2, 6-dioxy-pyrimidine 

Since  these  substances  do  not  yield  uric  acid  or  purine  bases 
their  fate  will  not  be  discussed  here. 

The  mode  of  origin  of  uric  acid  from  nucleic  acid  through  the 
purine  bases  is  as  follows : 

Nucleic  acid 


N  =  C— NH2 

I       I 
HC    C— NH 


>H 


N— C— N 

Adenine 
(6-amino  purine) 


HN— CO 

I  I 
H2NC    C— NH 

II  II        >CH 
N— C— N^ 

Guanine 
(2 -amino,  6-oxy  purine) 


HN— CO 

I  I 

HC    C— NH— > 

II  II        >CH 

N— C— N^ 

Hypoxanthine 
(6-oxy  purine) 


NH— CO 

I       I 
OC    C— NH— ^ 

I      II        >CH 
HN— C— N^ 

Xanthine 
(2,  6-dioxy  purine) 


HN— CO 

I       I 
OC    C— NH 

I    II      >co 

HN— C— NH 

Uric  acid 
(2,  6,  8-trioxy  purine) 


134  CHEMISTRY  OF  FOOD  AND   NUTRITION 

Not  only  is  uric  acid  the  most  highly  oxidized  of  the  purines, 
but  it  represents  the  highest  degree  to  which  oxidation  can  be 
carried  without  breaking  the  purine  ring.  The  extent  to  which 
the  purine  ring  is  broken  and  uric  acid  destroyed  in  the  body 
varies  with  the  species.  In  most  mammals  such  "  uricolysis  " 
is  an  important  feature  of  the  purine  metabolism.  In  man  the 
power  to  destroy  uric  acid  seems  to  have  been  almost  or  en- 
tirely lost,  many  recent  investigations  tending  to  show  that  the 
human  body  does  not  contain  uricolytic  enzymes  and  that 
all  of  the  uric  acid  formed  in  the  body  must  be  transported  and 
excreted  either  through  the  kidneys  (chiefly  in  the  form  of  acid 
urates)  or  through  the  intestinal  wall. 

Purines  undergoing  metabolism  in  the  body  may  be  derived 
either  (i)  from  the  catabolism  of  nucleoprotein  of  body  tissue 
or  (2)  from  the  food  which  may  contain  both  nucleoproteins 
and  free  purines.  Sometimes  the  term  "  endogenous  uric  acid  " 
is  applied  to  that  fraction  having  the  former  origin,  while  "  ex- 
ogenous uric  acid  "  indicates  that  fraction  which  is  directly  due 
to  the  food.  The  endogenous  uric  acid  in  the  urine  of  man  of 
average  size  amounts  usually  to  about  0.3  to  0.4  gram  per  day ; 
the  exogenous  varies  from  mere  traces  to  2  grams  or  more  accord- 
ing to  the  kind  and  amount  of  food  consumed.  On  ordinary 
mixed  diet  the  total  urinary  output  of  uric  acid  averages  about 
0.6  to  0.7  gram  per  man  per  day.  The  usual  range  is  about 
0.5  to  i.o  gram  of  uric  acid  per  man  per  day,  in  which  case  the 
uric  acid  nitrogen  constitutes  about  i  to  3  per  cent  of  the  total 
nitrogen  of  the  urine. 

Recent  investigations  of  Jones,  Levene,  and  others  have 
greatly  elaborated  the  theory  of  nucleic  acid  structure  and 
purine  metabohsm  outlined  above.  For  full  discussion  the 
reader  is  referred  to  the  works  of  Jones  (1914)  and  Jones  and 
Read  (1917). 

Creatine  and  creatinine.  —  Chemically  creatinine  is  the 
anhydride  of  creatine : 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      135 

N  (CH3)— CH2— C  =0  N  (CH3)— CH2— CO 

I  I  I 

HN  =  C  OH  HN  =  C 

I  I 

NH2  NH- 

Creatine  Creatinine 

The  biochemical  relationships  and  physiological  significance 
of  these  substances  have  been  much  studied  in  recent  years, 
and  the  literature  of  the  subject  is  far  too  extensive  to  be 
summarized  satisfactorily  here.  The  main  facts  with  regard  to 
their  ehmination  as  end  products  of  metabolism  are :  that  crea- 
tine appears  in  the  urine  of  children  normally  and  in  that  of 
adults  during  starvation,  fevers,  and  other  wasting  diseases 
and  when  there  is  impaired  functioning  of  the  liver;  that 
normal  adults  ordinarily  excrete  little  or  no  creatine  but  a 
considerable  amount  of  creatinine.  The  quantity  of  creatinine 
excreted  is  fairly  constant  for  the  individual,  averaging  about 
0.02  gram  per  kilogram  of  body  weight  per  day.  On  ordinary 
mixed  diet  the  creatinine  nitrogen  usually  constitutes  3  to  7 
per  cent  of  the  total  nitrogen  of  the  urine. 

Distribution  of  excreted  nitrogen  as  influenced  by  level  of  pro- 
tein metabolism.  —  The  above  statements  regarding  the  dis- 
tribution of  the  eliminated  nitrogen  among  the  different  end 
products  refer  to  results  obtained  upon  an  ordinary  mixed 
diet  containing  the  usual  amount  of  protein.  FoHn  has  shown 
by  a  careful  and  extended  study  of  the  urines  of  healthy  men 
living  first  upon  high  and  then  upon  low  protein  diets,  that  the 
distribution  of  the  nitrogen  between  urea  and  the  other  nitrog- 
enous end  products  depends  very  largely  upon  the  absolute 
amount  of  nitrogen  metabohzed.  In  the  case  of  a  man  who  on 
one  day  consumed  high  protein  diet  free  from  meat,  and  a  week 
later  was  Hving  on  a  diet  of  starch  and  cream,  which  furnished 
in  all  about  6  grams  of  protein  per  day,  the  distribution  of  end 
products  was  changed  as  shown  in  the  following  table: 


136 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


Total  nitrogen  .  . 
Urea  nitrogen  .  . 
Ammonia  nitrogen 
Uric  acid  nitrogen 
Creatinine  nitrogen 
Undetermined  nitrogen 


On  High  Protein  Diet 
(Free  from  Meat) 


Grams 


16.8 
14.7 
0.49 
0.18 
0.58 
0.85 


Per  cent 


87.5 
2.9 
I.I 
3.6 
4.9 


On  Low  Protein  Diet 
(Starch  and  Cream) 


Grams 


3-6 

2.2 

0.42 

0.09 

0.60 

0.27 


Per  cent 


61.7 
II-3 

2-5 
17.2 

7.3 


Thus,  on  passing  from  the  high  protein  to  the  low  protein  diet 
(both  being  free  from  meat  products)  there  was  a  marked  de- 
crease in  both  the  absolute  and  the  relative  amounts  of  urea, 
and  a  decrease  in  the  absolute,  but  increase  in  the  relative, 
amount  of  uric  acid,  while  the  absolute  amount  of  creatinine 
remained  unchanged,  so  that  its  relative  amount  was  greatly 
increased. 

REFERENCES 

Abderhalden.    Lehrbuch  der  Physiologische  Chemie,  Dritte  Aufl. 

Abel,  Rowntree  and  Turner.    The  Removal  of  Diffusible  Substances 

from  the  Circulating  Blood  of  Living  Animals  by  Dialysis.    Journal 

0}  Pharmacology,  Vol,  5,  page  275  (1913). 
AcKROYD  AND  HoPKiNS.     Feeding  Experiments  with  Deficiencies  in  the 

Amino  Acid  Supply :    Arginine  and  Histidine  as  Possible  Precursors 

of  Purines.    Biochemical  Journal,  Vol.  10,  pages  551-576  (December, 

1916). 
Allen.     Glycosuria  and  Diabetes. 
Benedict.    Uric  Acid   in   Its   Relations   to   MetaboHsm.    The   Harvey 

Lectures,  1915-1916. 
Dakin.     Oxidations  and  Reductions  in  the  Animal  Body. 
Dakin  and  Dudley.     (A  series  of  papers  on  intermediary  metabolism.) 

Journal  of  Biological  Chemistry,  Vol.  14,  pages  321,  423,  555;  Vol.  15, 

pages  127,  463;  Vol.  16,  page  505;  Vol.  17,  page  451;  Vol.  18,  page 

29  (1912-1913). 
Embden  and  Schmitz.     Synthesis  of  Amino  Acids  in  the  Liver.    Bio- 

chemische  Zeitschrift,  Vol.  29,  page  423;  Vol.  38,  page  393  (1910-1912). 


THE  FATE  OF  THE  FOODSTUFFS  IN  METABOLISM      137 

FoLiN.  A  Theory  of  Protein  Metabolism.  American  Journal  of  Physi- 
ology, Vol.  13,  page  117  (1905)- 

FoLiN  AND  Denis.  Protein  Metabolism  from  the  Standpoint  of  Blood  and 
Tissue  Analysis.  Journal  of  Biological  Chemistry,  Vol.  11,  pages  87, 
161;  Vol.  12,  pages  141,  253,  259;  Vol.  14,  page  29  (1912-1913). 

Henriqxjes  and  Andersen.  Nutrition  through  Intravenous  Injection. 
Zeitschrift  fur  physiologische  C hemic,  Vol.  88,  page  357  (191 3). 

Janney.  The  Metabolic  Relationship  of  the  Proteins  to  Glucose.  Journal 
of  Biological  Chemistry,  Vol.  20,  page  321 ;  Vol.  22,  page  203;  Vol.  23, 
page  77  (1915)- 

Jones.  Nucleic  Acids;  their  Chemical  Properties  and  ^Physiological 
Conduct  (1914). 

Jones  and  Read.  (On  the  structure  of  yeast  nucleic  acid.)  Journal  of 
Biological  Chemistry,  Vol.  29,  pages  111-122,  123-126;  Vol.  31,  page 

337  (1917). 

Knoop  and  Kertes.  Behavior  of  a-Amino  Acids  and  a-Ketonic  Acids 
in  the  Liver.  Zeitschrift  fiir  physiologische  Chemie,  Vol.  71,  page  252 
(1911). 

Levene  and  Meyer.  (Intermediary  metabolism  of  carbohydrate.)  Jour- 
nal of  Biological  Chemistry,  Vol.  11,  page  361 ;  Vol.  1 2,  page  265 ;  Vol.  14, 
pages  149,  551;  Vol.  15,  page  65;  Vol.  17,  page  442;  Vol.  18,  page 
469   (1912-1914). 

LuSK.     Science  of  Nutrition. 

Lyman.    Metabolism  of  Fats.    Journal  of  Biological  Chemistry,  Vol.  32, 

^     pages  7,  13  (191 7). 

Mathews.    Physiological  Chemistry,  Chapter  18. 

Pfluger.  Glycogen.  Arc hiv  fiir  die  gesammte  Physiologic,  Vol.  96,  pages 
1-398  (1903). 

Rose.  Creatinuria  in  Women.  Journal  of  Biological  Chemistry,  Vol.  31, 
page  I  (1917)- 

Underhill.  Studies  on  the  Metabohsm  of  Ammonium  Salts.  Journal 
of  Biological  Chemistry,  Vol.  15,  pages  327,  337,  341  (1913). 

Van  Slyke.  The  Significance  of  Amino  Acids  in  Physiology  and  Pa- 
thology.   Harvey  Lectures,  1915-1916. 

Van  Slyke  et  al.  The  Fate  of  Protein  Digestion  Products  in  the  Body. 
Journal  of  Biological  Chemistry,  Vol.  12,  page  399;  Vol.  16,  pages  187, 
197,  213,  231  (1912-1913).  Proceedings  of  the  Society  for  Experimental 
Biology  and  Medicine,  Vol.  12,  page  93  (191 5). 

Wells.     Chemical  Pathology. 

WooDYATT.  Studies  on  Intermediary  Carbohydrate  Metabohsm.  Harvey 
Lectures,  1915-1916. 


CHAPTER  VI 

THE  FUEL  VALUE  OF  FOOD  AND  THE  ENERGY 
REQUIREMENT  OF  THE  BODY 

We  have  seen  that  carbohydrate  after  Its  absorption  into 
the  body  may  either  be  oxidized,  or  stored  as  glycogen,  or  trans- 
formed into  fat ;  that  fat  may  be  oxidized  or  stored  and  that  at 
least  its  glyceryl  radicle  may  be  converted  into  carbohydrate ; 
and  that  protein  absorbed  as  amino  acids  may  either  be  built 
up  into  body  protein,  or  deaminized  and  oxidized,  or  may  yield 
carbohydrate,  or  may  (either  directly  or  indirectly)  contribute 
to  the  production  of  fat.  It  has  also  been  shown  that  any  or 
all  of  these  foodstuffs  may  be  utilized  as  fuel  for  muscular 
work. 

Thus  the  body  is  not  restricted  to  the  use  of  any  one  food- 
stuff for  the  support  of  any  one  kind  of  work,  but  on  the  contrary 
has  very  great  power  to  convert  one  nutrient  into,  or  use  it  in 
place  of,  another,  and  so  to  utilize  its  resources  that  the  total 
potential  energy  of  all  of  these  nutrients  is  economically  em- 
ployed to  support  the  work  of  all  parts  of  the  organism.  The 
carbohydrates,  fats,  and  proteins  stand  in  such  close  mutual 
relations  in  their  service  to  the  body  that  for  many  purposes 
we  may  properly  consider  the  food  as  a  whole  with  reference 
to  the  total  nutritive  requirements,  provided  a  common  meas- 
ure of  values  and  requirements  can  be  found.  Since  the 
most  conspicuous  nutritive  requirement  is  that  of  energy  for 
the  work  of  the  body,  and  since  these  organic  nutrients  all 

138 


THE  FUEL  VALUE  OF  FOOD  1 39 

serve  as  fuel  to  yield  this  energy,  the  best  basis  of  comparison 
is  that  of  fuel  value,  expressed  most  conveniently  in  terms  of 
Calories. 

Heats  of  Combustion  of  the  Foodstuffs 

The  calorific  value  or  heat  of  combustion  of  any  substance, 
i.e. .  the  amount  of  energy  liberated  by  the  burning  of  a  given 
quantity  of  the  combustible  material,  is  best  determined  by 
means  of  the  bomb  calorimeter  devised  by  Berthelot.  The 
particular  form  of  Berthelot  bomb  which  has  been  most  used 
in  the  examination  of  food  materials  and  physiological  products 
is  that  of  Atwater  and  •  Blakeslee,  fully  described  by  Atwater 
and  Snell  in  the  Journal  of  the  American  Chemical  Society  for 
July,  1903.  In  outline  it  consists  of  a  heavy  steel  bomb  with 
a  platinum  or  gold-plated  copper  Hning  and  a  cover  held  tightly 
in  place  by  means  of  a  strong  screw  collar.  A  weighed  amount 
of  sample  is  placed  in  a  capsule  within  the  bomb,  which  is  then 
charged  with  oxygen  to  a  pressure  of  at  least  20  atmospheres 
(300  pounds  or  more  to  the  square  inch),  closed,  and  immersed 
in  a  weighed  amount  of  water.  The  water  is  constantly  stirred 
and  its  temperature  taken  at  intervals  of  one  minute  by  means 
of  a  differential  thermometer  capable  of  being  read  to  one 
thousandth  of  a  degree.  After  the  rate  at  which  the  temperature 
of  the  water  rises  or  falls  has  been  determined,  the  sample 
is  ignited  by  means  of  an  electric  fuse,  and,  on  account  of  the 
large  amount  of  oxygen  present,  undergoes  rapid  and  complete 
combustion.  The  heat  liberated  is  communicated  to  the  water 
in  which  the  bomb  is  immersed,  and  the  resulting  rise  in  tem- 
perature is  accurately  determined.  The  thermometer  read- 
ings are  also  continued  through  an  *'  after  period,"  in  order 
that  the  "radiation  correction"  may  be  calculated  and  the 
observed  rise  of  temperature  corrected  accordingly.  This 
corrected  rise,  multipHed  by  the  total  heat  capacity  of  the  ap- 
paratus and  the  water  in  which  it  is  immersed,  shows  the  total 


I40 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


heat  liberated  in  the  bomb.     From  this  must  be  deducted  the 
heat  arising  from  accessory  combustions  (the  oxidation  of  the 

iron  wire  used  as  a 
fuse,  etc.)  to  ob- 
tain the  number  of 
Calories  *  arising 
from  the  combus- 
tion of  the  sample. 
More  recently 
the  adiabatic  form 
of  the  bomb  cal- 
orimeter (a  modifi- 
cation which  avoids 
the  necessity  of  cor- 
rections for  heat 
loss)  is  coming  into 
more  general  use. 
See,  for  example, 
the  paper  by  Riche, 
in  the  Journal  of  the 
American  Chemical 
Society  for  Novem- 
ber, 1913. 

♦When  the  term  "Cal- 
orie" is  used  in  this  work 
it  will  be  understood  to 
mean  the  "greater  cal- 
orie," or  "kilogram  cal- 
orie," i.e.  the  amount  of 
heat  required  [to  raise 
the  temperature  of  one 
kilogram  of  water  one 
degree  centigrade.  This 
is  very  nearly  the  same 
as  the .  heat  required  to 
raise  four  pounds  of  water 
Fig.  6.  —  The  Atwater  bomb  calorimeter.  one  degree  Fahrenheit. 


THE  FUEL  VALUE  OF  FOOD  141 

The  heat  of  combustion  of  organic  substances  is  closely 
connected  with  their  elementary  composition.  One  gram 
of  carbon  burned  to  carbon  dioxide  yields  8.08  Calories  and 
I  gram  of  hydrogen  burned  to  water  yields  34.5  Calories.  If 
a  compound  consisting  of  carbon  and  hydrogen  only  be  burned, 
it  gives  nearly  the  amount  of  heat  which  these  would  give  if 
burned  separately. 

On  the  other  hand,  carbohydrates  and  fats,  being  com- 
posed of  carbon,  hydrogen,  and  oxygen,  the  carbon  and 
hydrogen  are  already  partly  oxidized  by  the  oxygen  present 
in  the  molecule ;  so  that  100  grams  of  glucose,  for  example, 
containing  40  grams  carbon,  6.7  grams  hydrogen,  and  53.3 
grams  oxygen,  would  yield  considerably  less  heat  than  would 
be  obtained  by  burning  40  grams  of  pure  carbon  and  6.7 
grams  of  pure  hydrogen  to  carbon  dioxide  and  water  respec- 
tively. 

Proteins  when  burned  in  the  calorimeter  give  off  their 
carbon  as  carbon  dioxide,  their  hydrogen  as  water,  and 
their  nitrogen  as  nitrogen  gas.*  Thus  the  nitrogen  con- 
tributes nothing  to  and  takes  nothing  from  the  heat  of  com- 
bustion; and  the  latter  is  dependent  here,  as  in  the  case  of 
carbohydrates  and  fats,  upon  the  amount  of  carbon  and 
hydrogen  present  and  the  extent  to  which  they  are  already 
combined  with  oxygen.  A  Httle  additional  heat  is  obtained 
by  the  burning  of  the  small  amount  of  sulphur  present  in  the 
protein. 

The  relation  between  the  elementary  composition  and  heat 
of  combustion  will  be  made  clearer  by  the  following  table, 
which  includes  a  number  of  typical  compounds  found  in  the 
food  or  formed  in  the  body. 

*  As  a  matter  of  fact  a  small  part  of  the  nitrogen  is  oxidized  to  nitric  acid  in 
the  bomb  calorimeter,  but  this  is  determined  and  its  heat  of  formation  subtracted, 
so  that  the  final  results  are  as  stated  above. 


142 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


Heats  of  Combustion  and  Approximate  Elementary  Composition  of 
Typical  Compounds 


Substance 

Heat  of 

COMBUS- 
TION 

Calories 

PER  GRAM 

Carbon 

PER 
CENT 

Hydro- 
gen 

PER 
CENT 

Oxygen 

PER 
CENT 

Nitro- 
gen 

PER 

CENT 

Sul- 
phur 

PER 

CENT 

Phos- 
phorus 

PER 

CENT 

Glucose      

3-75 

40.0 

6.7 

53.3 

Sucrose 

3.96 

42.1 

6.4 

51-5 

Starch 
Glycogen 

4.22 

44.4 

6.2 

49-4 

Body  fat    . 

9.60 

76.5 

12.0 

II-5 

Butter  fat 

9.30 

75-0 

II. 7 

13-3 

Edestin 

s•62^ 

51.4 

7.0 

22.1 

18.6 

0.9 

Legumin 

S.62 

51-7 

7.0 

22.9 

18.0 

0.4 

Gliadin 

5.74 

52.7 

6.9 

21.7 

17.7 

I.O 

Casein  . 

It 

53-1 

7.0 

22.5 

15.8 

0.8 

0.8 

Albumin 

52.5 

7.0 

23.0 

16.0 

1-5 

Gelatin 

I5-30 

50.0 

6.6 

24.8 

18.0 

0.6 

Creatinine 

4.58 

42.S 

6.2 

14.1 

37.2 

Urea      .     . 

2.53 

20.0 

6.7 

26.7 

46.6 

Since  the  energy  used  in  the  body  is  obtained  from  the  oxi- 
dation of  the  same  kinds  of  compounds  which  exist  in  food, 
i.e.  from  carbohydrates,  fats,  and  proteins  (or  their  cleavage 
products),  we  can  estimate  the  amount  of  energy  transformed  in 
the  body  if  we  know  the  amount  of  each  kind  of  foodstuff  oxi- 
dized. Account  must,  however,  be  taken  of  the  completeness 
of  the  oxidation  in  each  case. 

When  undergoing  complete  oxidation  in  the  bomb  calorimeter 
the  foodstuffs  yield  the  following  average  heats  of  combustion : 


Carbohydrates 

Fats 

Proteins 


4.1  Calories  per  gram. 
9.45  Calories  per  gram. 
5.65  Calories  per  gram. 


In  the  body  carbohydrates  and  fats  are  oxidized  to  the  same 
products  as  in  the  calorimeter  and  so  yield  the  same  amounts 
of  heat.  Protein,  however,  which  burns  in  the  bomb  to  carbon 
dioxide,  water,  and  nitrogen,  yields  in  the  body  no  free  nitrogen. 


THE  FUEL  VALUE  OF  FOOD  143 

but  urea  and  other  organic  nitrogen  compounds  which  are 
ehminated  as  end  products.  These  organic  nitrogenous  end 
products  are  combustible ;  they  represent  a  less  complete  oxi- 
dation of  protein  in  the  body  than  takes  place  in  the  bomb. 
The  loss  of  potential  energy  calculated  on  the  assumption  that 
all  nitrogen  left  the  body  as  urea  would  be  about  0.9  Calorie 
per  gram  of  protein,  but  on  account  of  the  elimination  of  other 
substances  of  higher  heat  of  combustion  (creatinine,  uric  acid, 
etc.),  the  actual  loss  in  the  form  of  combustible  end  products  is 
considerably  greater  and  averages  about  1.3  Calories  for  each 
gram  of  protein  broken  down  in  the  body. 

Hence,  when  the  body  burns  material  which  it  has  previously 
absorbed,  it  obtains : 

From  carbohydrates  4.1    Calories  per  gram. 

From  fats  9.45  Calories  per  gram. 

From  protein  (5.65  —  1.30  =  )       4.35  Calories  per  gram. 

In  calculating  the  fuel  value  of  the  food,  however,  allow- 
ance must  be  made  for  the  fact  that  a  part  of  each  of  the  ma- 
terials is  lost  in  digestion.* 

The  approximate  averages  on  a  mixed  diet  are : 

Carbohydrates     2%  lost,  98%  absorbed. 
Fats  5%  lost,  95%  absorbed. 

Protein  8%  lost,  92%  absorbed. 

The  approximate  physiological  fuel  values  of  the  food  constit- 
uents are  then: 

Carbohydrates  4.1    X  98%  =  4.  Calories  per  gram. 
Fats  9-45  X  95%  =  9.  Calories  per  gram. 

Protein  4.35  X  92%  =4.  Calories  par  gram. 

The  figures  given  by  Rubner  as  representing  the  fuel  values  of  food  con- 
stituents are  as  follows  :  *""" 
Carbohydrates    4.1 
Fats                     9.3 
Protein                4.1 

*  The  expression  "  lost  in  digestion"  is  here  used  in  the  sense  explained  in  Chapter 
IV. 


144  CHEMISTRY  OF  FOOD  AND   NUTRITION 

These  were  derived  from  experiments  with  dogs  fed  on  meat,  starch, 
sugar,  etc.,  and  therefore  do  not  allow  for  so  much  loss  in  digestion  as  has 
been  found  to  occur  with  men  living  on  ordinary  mixed  diet. 

Fuel  Value  of  Food  Materials 

If  the  composition  of  a  food  is  known,  its  approximate  fuel 
value  is  easily  computed  by  means  of  the  above  factors.  Thus 
milk  of  about  average  composition  contains : 

Protein,  3.3  per  cent;  fat,  4.0  per  cent;  carbohydrate,  5.0 
per  cent. 
One  hundred  grams  of  such  milk  will  furnish  in  the  form  of 
protein  {^.^  X  4.  =)  13.2  Calories;  of  fat  (4.0  X  9.  =)  36.0 
Calories;  of  carbohydrate  (5.0  X  4.  =  )  20.0  Calories;  total 
for  100  grams  of  milk,  69.2  Calories. 

Eggs  contain  *  on  the  average,  in  the  edible  portion,  13.4 
per  cent  protein,  10.5  per  cent  fat,  and  no  appreciable  amount 
of  carbohydrate.  They  would  then  furnish  per  100  grams 
(13.4  X  4)  +  (io-5  X  9)  =  148.1  Calories. 

Milk  and  eggs  are  sufficiently  similar  to  be  used  interchange- 
ably in  the  adult  dietary  within  reasonable:  Hmits,  but  evi- 
dently they  furnish,  weight  for  weight,  very  different  amounts 
of  nutrients  and  energy.  Ordinarily  the  quantities  to  be 
taken  as  equivalent  or  mutually  replaceable  are  those  which 
furnish  equal  fuel  value,  e.g.  loo-Calorie  portions,  the  weights 
of  which  may  be  calculated  directly  from  the  fuel  values  of  100 
grams. 

Thus,  for  milk  —  100  grams  furnish  69.2   Calories;    then, 
if  X  be  the  number  of  grams  which  furnish  100  Calories : 
100:  69.2  ::  :j:::  100;     x  =  i4$.'f 

Similarly  for  eggs: 

100 :  148  ::x:  100 ;    x  =  6S% 

*  These  and  all  similar  statements  of  average  composition  are  based  on  Bull. 
28,  Office  of  Experiment  Stations,  U.  S.  Dept.  Agriculture. 

t  It  is  considered  sufficiently  accurate  to  state  these  quantities  to  the  nearest 
whole  number  of  grams. 


THE  FUEL  VALUE  OF  FOOD 


US 


And  since  the  two  extremes  in  the  proportion  are  always  the 
same,  the  weight  in  grams  of  the  loo-Calorie  portion  may  al- 
ways be  found  by  dividing  10,000  (the  product  of  the  extremes) 
by  the  number  of  Calories  per  100  grams. 

The  fuel  value  of  foods  is  often  stated  in  Calories  per  pound. 
Thus  in  the  same  table  (Bull.  28)  from  which  the  above  figures 
for  composition  are  taken,  the  fuel  value  of  milk  is  given  as 
325  Calories  per  pound.  Since  453.6  grams  furnish  325  Calo- 
ries, — 

453.6 :  325  :::jf:  1,00;    x  =  139.6, 

the  number  of  grams  required  to  furnish  100  Calories.  This 
figure  is  about  3  per  cent  less  than  the  one  found  above  be- 
cause it  is  based  on  a  fuel  value  computed  by  Rubner's  factors, 
which  are  2.5  to  3.3  per  cent  higher  than  the  factors  based  on 
more  recent  work.      (See  above.) 

It  The  following  figures  for  a  few  common  food  materials  * 
are  based  upon  the  more  recent  factors,  and  show  the  weight  of 
the  loo-Calorie  portion  in  grams  and  ounces,  and  the  distribu- 
tion of  the  calories  between  proteins,  fats,  and  carbohydrates : 


Table  of  ioo-Calorie  Portions  f  of  Food  Material  Based  on  the 
Factors  —  Protein,  4;  Fat,  9;  Carbohydrate,  4 


Food  Material 
(Edible  Portion) 

Weight  of  Portion 

Distribution  of  Calories 

Grams 

Ounces 

In  protein 

In  fat 

In  carbo- 
hydrates 

Beef,  free  from  visible  fat     . 
Beef,  round  steak    .... 

Beef,  corned 

Ham,  lean 

Ham,  fat 

86 
64 
S3 
37 
19 

3-0 
2.3 
1-3 
1.2 
0.7 

80.4 
54-5 
20.9 
29.7 
II. I 

19.6 
45-5 
79.1 
70.3 
88.9 

*  Arranged  according  to  the 
Department  of  Agriculture  and 
der  Menschlichen  Nahrungs-  und 
grain  products,  sugars  and  starch 

t  Table  i  of  Appendix  B  shov 
food  materials. 
L 

classificat 
in  Konig' 
Genussmit 
es,  vegeta 
rs  ioo-Cal( 

ion  used 
3  welI-kno\ 
tel,  viz.  m( 
bles,  fruits 
jrie  portioi 

in  the  bul 
vn  referen 
iats,  fish,  ( 
,  nuts,  oih 
is  of  a  mu 

letins  of 
ce  work  D 
;ggs,  dairy 

ch  larger 

the  U.  S. 
ie  Chemie 
products, 

number  of 

146 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


Table  of  ioo-Calorie  PoRxiONsf  of  Food  Material  Based  on  the 
Factors  —  Protein,  4;  Fat,  9;  Carbohydrate,  4     (Continued) 


Food  Material 
(Edible  Portion) 


Bacon,  smoked   .     .     . 

Codfish 

Salmon 

Eggs 

Milk 

Butter 

Corn  meal      .     .     .     . 

Oatmeal 

Rice 

Wheat,  "entire"      .     . 

Wheat  flour 

Bread,  white       .     ,     . 

Sugar         

Asparagus  .  .  .  . 
Beans,  dried  .  .  .  . 
Beans,  string       .     .     . 

Beets 

Cabbage    

Carrots 

Celery 

Corn,  green  or  canned 

Lettuce 

Potatoes 

Spinach 

Tomatoes 

Turnips      .     .     .     .     , 

Apples , 

Bananas  .... 
Currants,  dried  .  . 
Oranges  .... 
Peaches  .... 
Pineapple  .... 

Plums 

Prunes,  dried  .  . 
Raisins  .... 
Almonds  .... 
Chestnuts  .  .  . 
Peanuts  .... 
Olive  Oil    .... 


Weight  of  Portion 


Grams        Ounces 


Distribution  of  Calories 


In  protein 


16 

0.6 

6.7 

93-3 

143 

5-0 

95-0 

5-0 

49 

1-7 

43-3 

56.7 

67 

2.3 

36.1 

63.9 

145 

5-1 

19.0 

52.0 

14 

0.5 

0.5 

99-5 

27 

I.O 

9.0 

11.4 

25 

0.9 

16.1 

16.2 

28 

1.0 

9.1 

0.7 

28 

1.0 

14.7 

3.5 

28 

1.0 

11.8. 

2.8 

38 

1.3 

14.1 

4-5 

25 

0.9 

450 

16.0 

32.4 

8.2 

29 

1.0 

26.1 

4.7 

240 

8.4 

22.2 

6.5 

216 

7.4 

13.8 

2.0 

317 

II. I 

20.3 

8.6 

220 

7-7 

9-7 

7.9 

540 

19.1 

23.8 

4.8 

99 

3-2 

12.2 

9.8 

523 

18.4 

25.2 

14.1 

120 

4.2 

10.5 

1.2 

418 

14.7 

35-1 

II-3 

438 

15.5 

15-7 

15.7 

253 

8.9 

13-2 

4.6 

159 

5.6 

2.5 

7.2 

lOI 

3-5 

5-2 

5.4 

31 

I.I 

3-0 

4-7 

194 

6.8 

6.2 

3-5 

242 

8.5 

6.8 

2.2 

232 

8.2 

3-7 

6.3 

118 

4.1 

4-7 

23 

1.2 

2.8 

29 

1.0 

3-0 

8.6 

15 

0.5 

I3-0 

76.4 

43 

1-5 

10.7 

16.6 

18 

0.6 

18.8 

63.4 

II 

0.4 

lOO.O 

In  fat 


THE  FUEL  VALUE  OF  FOOD 

Since  proteins  and  carbohydrates  have  the  same  average 
fuel  value  and  the  ash  of  food  does  not  as  a  rule  constitute  a 
large  percentage,  the  striking  differences  in  the  weights  of  the 
various  foods  required  to  furnish  loo  Calories  are  usually- 
referable  to  differences  in  water  content  or  fat  content  or  both. 
That  beans  have  nearly  20  times  the  fuel  value  of  celery  is 
essentially  due  to  the  difference  in  moisture,  while  the  differ- 
ence in  fuel  value  between  lean  beef  and  bacon,  or  between 
codfish  and  salmon,  is  chiefly  a  matter  of  fat  content..  Meat 
free  from  fat  is  about  three  fourths  water  and  one  fourth  pro- 
tein, and  so  has  a  fuel  value  of  about  one  Calorie  per  gram,  while 
clear  fat  has  a  fuel  value  about  nine  times  as  great. 

Fuel  values  of  meats  as  given  in  the  standard  tables  are  apt 
to  be  somewhat  misleading,  inasmuch  as  they  allow  for  all  the 
fat  ordinarily  found  on  the  various  cuts  as  taken  from  the 
animal,  whereas  in  many  cases  a  considerable  part  of  this  fat 
is  trimmed  off  by  the  butcher  and  treated  as  a  by-product; 
and  often  much  of  the  remaining  fat  is  removed  either  in  the 
kitchen  or  at  the  table.  If  a  pound  of  steak  consists  of  14 
ounces  of  clear  lean,  and  2  ounces  of  clear  fat,  and  the  fat  is 
not  eaten,  at  least  half  of  the  total  fuel  value  of  the  pound  of 
steak  is  lost. 

Many  vegetables  are  more  watery  than  lean  meats  and  so 
contrast  even  more  strikingly  with  the  fats.  An  ounce  of  clear 
fat  pork  is  equal  in  fuel  value  to  about  two  pounds  of  cabbage ; 
an  ounce  of  olive  oil  to  over  three  pounds  of  lettuce. 

In  connection  with  such  comparisons  of  fuel  value,  however, 
it  should  be  emphasized  that  the  fuel  value  of  a  food,  while  of 
primary  importance,  is  not  alone  a  complete  measure  of  its 
nutritive  value,  which  will  depend  in  part  also  upon  the  amounts 
and  forms  of  nitrogen,  phosphorus,  iron,  and  various  other 
essential  elements  furnished  by  the  food. 

In  order  to  indicate  relative  richness  in  nitrogenous  constituents  (pro- 
tein), it  is  not  uncommon  to  state  the  "nutritive  ratio"  along  with  the  fuel 


148  CHEMISTRY  OF  FOOD  AND  NUTRITION 

value  of  a  food.  The  "nutritive  ratio"  or  "nutrient  ratio"  is  the  ratio  of 
non-nitrogenous  to  nitrogenous  nutrients,  compared  on  the  basis  of  fuel 
values.  Since  the  fuel  values  of  carbohydrates  and  protein  are  taken  as 
equal  (4  Calories  per  gram),  and  that  of  fats  as  2|  times  as  great  (9  Calories 
per  gram),  the  nutritive  or  nutrient  ratio  may  be  shown  as  follows : 

Carbohydrate  +  2^  Fat  :  Protein  ::x  :  i ; 
or  the  ratio  may  be  expressed  in  the  form  of  a  fraction : 

Carbohydrate  +  2^  Fat 
Protein 

These  expressions  can,  of  course,  be  applied  equally  well  to  percentages  or 
to  weights  of  nutrients. 

The  same  information  as  is  given  by  the  statement  of  fuel  value  per  pound 
and  nutritive  ratio  may  be  obtained  by  comparing  the  weight  of  loo-Calorie 
portions  and  the  percentages  of  calories  supplied  by  protein  as  shown  in  the 
above  table.  The  statement  that  19  per  cent  of  the  calories  of  milk  are 
furnished  by  protein  is  equivalent  to  giving  the  nutritive  ratio  of  milk  as  4.3. 


ENERGY  REQUIREMENT  IN  METABOLISM  — METHODS  OF 
STUDY  AND  AMOUNTS  REQUIRED  FOR  MAINTENANCE 
AT  REST 

We  know  definitely  from  accurate  experiments  that  the 
"  physiological  fuel  values  "  which  have  been  deduced  repre- 
sent the  energy  which  is  actually  obtained  by  the  body  from 
the  food  and  which  appears  as  muscular  work  or  as  heat; 
and  we  have  every  reason  to  suppose  that  under  ordinary 
conditions  the  carbohydrates,  fats,  and  proteins  each  supply 
the  body  with  the  kinds  of  energy  needed  for  its  maintenance 
and  for  its  work,  approximately  in  proportion  to  their  fuel 
values  as  calculated  above.  We  do  not  now  beheve  that  any 
one  nutrient  is  used  to  the  exclusion  of  others  as  a  source  of 
energy  for  any  particular  function,  nor  indeed  that  the  body 
makes  any  particular  distinction  between  the  foodstuffs  as 
sources  of  energy.  The  fuel  value  of  the  diet  as  a  whole  is 
utihzed  to  meet  the  energy  requirements  of  the  whole  body. 
For  the  present,  therefore,  it  is  the  fuel  value  of  the  day's 


THE  FUEL  VALUE  OF  FOOD  149 

dietary  which  we  have  to  consider  rather  than  the  distribution 
of  this  as  regards  protein,  fats,  and  carbohydrates. 

The  total  food  (or  energy)  requirement  is  best  expressed  in 
Calories  per  day,  either  for  the  whole  body  or  per  kilogram  of 
body  weight,  and  for  convenience  of  discussion  it  is  usually 
assumed  that  the  average  body  weight  (without  clothing)  is 
for  men  70  kilograms  (154  pounds)  and  for  women  eight  tenths 
as  much,  56  kilograms  (123  pounds). 

There  are  four  important  methods  of  studying  the  food 
requirements  of  man :  * 

1.  By  observing  the  amount  of  food  consumed  (dietary 
studies). 

2.  By  observing  the  amount  of  oxygen  consumed  —  pref- 
erably also  the  respiratory  quotient  (respiration  experiments). 

3.  By  determining  the  balance  of  intake  and  output  (car- 
bon and  nitrogen  metabolism  experiments). 

4.  By  direct  measurement  of  heat  given  off  by  the  body 
(calorimeter  experiments). 

Dietary  studies.  —  Most  dietary  studies  give  little  more 
than  a  general  indication  of  the  food  habits  of  the  people 
studied;  but  in  cases  where  persons  have  maintained  for  a 
long  time  the  same  dietary  habits  and  other  conditions  of  life, 
and  the  body  weight  has  remained  practically  constant,  it 
may  be  fairly  safe  to  assume  that  the  food  has  furnished  just 
about  the  right  amount  of  energy  for  the  maintenance  of  the 
body  under  the  observed  conditions. 

Great  care  must  be  taken  in  drawing  inferences  from  the 
body  weight  because  of  the  readiness  with  which  the  body 
gains  or  loses  moisture.  Athletes  often  lose  2  or  3  pounds  in 
an  hour  of  vigorous  exercise  and  regain  it  in  less  than  a  day. 
Gain  or  loss  of  body  weight  during  short  periods,  therefore, 

*  For  an  account  of  the  historical  development  of  the  principles  which  underiie 
the  measurement  of  metabolism,  see  the  introductory  chapter  of  Lusk's  Elements 
of  the  Science  of  Nutrition. 


150  CHEMISTRY  OF  FOOD  AND   NUTRITION 

does  not  by  any  means  necessarily  imply  a  corresponding 
gain  or  loss  of  fat.  The  body  may  lose  fat  and  at  the  same 
time  maintain  its  weight  through  gaining  water,  or  vice  versa. 
When,  however,  the  weight  remains  nearly  the  same  for  months 
at  a  time,  it  may  usually  be  assumed  that  there  is  no  impor- 
tant gain  or  loss  of  tissue  and  that  the  body  is  receiving  just  about 
the  proper  amount  of  total  food  for  its  needs.  Under  these 
conditions  an  accurate  observation  of  the  food  consumed  may 
give  valuable  indications  as  to  the  actual  food  requirement. 
Of  such  dietary  studies  perhaps  the  most  useful  individual  ex- 
ample is  that  of  Neumann,  who  reduced  his  diet  to  what  ap- 
peared to  be  just  about  sufficient  for  his  needs  and  then  recorded 
all  food  and  drink  taken  during  a  period  of  10  months  in  which 
the  body  weight  remained  nearly  constant.  The  average 
daily  food  furnished :  * 

Nutrients  Factors    Calories    '^'^^l^^'f^^^^ 

Protein  ......      66.1  grams  X  4-  =     264.4  1 

Fat 83.5  grams  X  9.  =     751-5  [  2242 

Carbohydrate  t    .     •     •     306.5  grams  X  4-  =    1226.0  J 

The  2242  Calories  per  day  were  evidently  fully  sufficient 
to  meet  the  energy  requirements  of  this  man,  whose  weight 
was  66.5  to  67  kilograms  (about  147  pounds)  and  who  was  en- 
gaged at  his  usual  (mainly  sedentary)  professional  work  in  the 
Hygienic  Institute  at  Kiel. 

Later,  when  his  weight  had  increased  to  71.5  kilograms  (157 
pounds)  as  the  result  of  following  for  a  time  a  more  liberal 
diet  (furnishing  about  2600  Calories  per  day),  he  again  observed 
*his  dietary  while  taking  what  was  supposed  to  be  an  amount  of 
food  sufficient  for  the  maintenance  of  the  body  and  no  more. 
This  second  dietary  study  was  continued  for  8  months,  during 
which  the  average  daily  food  consumption  was  found  to  be : 

*  The  data  are  taken  from  Chittenden's  Nutrition  of  Man,  page  286. 
t  Including  some  alcohol  (taken   in  the  form  of  beer),  which  is  estimated  as 
equivalent  in  fuel  value  to  1.75  times  its  weight  of  carbohydrates. 


THE  FUEL  VALUE  OF  FOOD  1 51 


NxjTRiENTS  Factors  Calories 


Total  Calories 
PER  Day 


Protein 76.2  grams  X  4.  =  304.8 

Fat 109.0  grams  X  9.  =  981.0  ^  2000 

Carbohydrates*.     .     .     178.6  grams  X  4.  =  714.4 

The  body  weight  remained  nearly  constant. 

These  results  indicate  that  this  subject,  a  man  of  average 
size,  living  a  normal  professional  Ufe  involving  no  manual 
labor  in  the  ordinary  sense,  but  not  excluding  such  muscular 
movements  as  are  naturally  incidental  to  a  sedentary  occupa- 
tion, found  his  energy  requirements  satisfied  with  food  furnish- 
ing 2000  to  2250  Calories  per  day. 

Respiration  experiments.  —  Since  the  foodstuffs  yield  their 
energy  through  being  oxidized  in  the  body,  it  is  evident  that  a 
measure  of  the  energy  metabolism  can  be  obtained  by  finding 
either  the  amount  of  foodstuffs  oxidized  or  the  amount  of  oxy- 
gen which  is  consumed  in  the  process.  The  apparatus  devised 
and  used  by  Zuntz  for  this  purpose  provides  a  mask,  fitting  air- 
tight over  the  mouth  and  nose  and  connected  by  means  of 
valved  pipes  with  apparatus  for  measuring  and  analyzing  the 
inspired  and  expired  air.  In  this  way  one  can  determine  the 
volume  of  oxygen  entering,  and  the  volume  leaving,  the  lungs. 
The  difference  is  the  volume  consumed  in  the  body. 

Benedict  has  devised  an  improved  form  of  respiration  ap- 
paratus in  which  the  subject  breathes,  either  through  a  mouth- 
or  nose-piece,  from  a  current  of  air  which  is  purified  and  kept 
in  circulation  in  the  same  manner  as  that  of  the  respiration 
calorimeter  chamber  described  below.  The  carbon  dioxide 
which  the  man  produces  is  absorbed  quantitatively  and  the 
oxygen  which  he  consumes  is  exactly  replaced  by  admitting 
measured  volumes  of  analyzed  oxygen  gas  from  a  cylinder  of 
compressed  oxygen. 

*  Including  some  alcohol  (taken  in  the  form  of  beer),  which  is  estimated  as 
equivalent  in  fuel  value  to  1.75  times  its  weight  of  carbohydrates. 


152  CHEMISTRY  OF  FOOD  AND  NUTRITION 


A  given  volume  of  oxygen  used  in  the  body  may  liberate 
somewhat  different  amounts  of  heat,  according  as  it  oxidizes 
fat,  carbohydrate,  or  protein.  For  accurate  estimations  of 
the  energy  liberated  it  is  therefore  necessary  to  know  the  kind 

Spirometer 


Lungs 


L 


Pump 


Absorbed 


Absorbed 


Fig.  7.  —  Diagram  of  Benedict  respiration  apparatus. 

Benedict. 


Courtesy  of  Dr.  F.  G. 


of  material  oxidized,  as  well  as  the  amount  of  oxygen  con- 
sumed.    This  is  calculated  from  the  respiratory  quotient. 

Since  the  amount  of  protein  broken  down  in  the  body  can 
be  estimated  from  the  nitrogen  excretion,  the  determination  of 
the  respiratory  quotient  along  with  the  oxygen  consumption 
shows  the  extent  of  the  combustion  in  the  body  and  the  pro- 


THE  FUEL  VALUE  OF  FOOD 


153 


portions  of  fat  and  carbohydrate  burned.*    From  these  data 
the  energy  can  be  calculated. 

As  a  matter  of  fact  it  is  not  necessary  to  go  through  the 
actual  calculation  of  the  amounts  of  fat  and  carbohydrate 
burned  since  the  energy  derived  from  a  liter  of  oxygen  when 
used  to  burn  carbohydrate  and  fat  in  different  proportions 
can  be  calculated  once  for  all  and  expressed  in  relation  to  the 
respiratory   quotient  as  shown  in   the  accompanying   table. 

Energy  Values  of  Oxygen  and  Carbon  Dioxide  at  Different 
Respiratory  Quotients  (Zuntz  and  Schumberg) 


Respiratory 
Quotient 

Calories 

Calories 

Calories 

PER  Liter  of 

PER  Liter  of 

per  Gram  of 

Oxygen 

Carbon  Dioxide 

Carbon  Dioxide 

0.70 

4.686 

6.694 

3.408 

0.71 

4.690 

6.606 

3.363 

0.72 

4.702 

6.531 

3.325 

0.73 

4.714 

6.458 

3.288 

0.74 

4.727 

6.388 

3.252 

0.7S 

4-739  X 

6.319  ^ 

3.217 

0.76 

4.752 

6.253 

3.183 

0.77 

4.764 

6.187 

3.150 

0.78 

4.776 

6.123 

3.117 

0.79 

4.789 

6.062 

3.086 

0.80 

4.801 

6.001 

3.055 

0.81 

4.813 

5.942 

3.025 

0.82 

4.825 

5.884 

2.996 

0.83 

4.838 

5.829 

2.967 

0.84 

4.850 

5.774 

2.939 

0.8s 

4.863 

5-721 

2.912 

0.86 

4.875 

5.669 

2.886 

0.87 

4.887 

5.617 

2.860 

0.88 

4.900 

5.568 

2.835 

0.89 

4.912 

5.519 

2.810 

*  Or,  with  very  little  error,  it  may  be  assumed  that  15  per  cent  of  the  oxygen 
goes  to  bum  protein  and  the  rest  is  divided  between  fat  and  carbohydrate.  The 
values  given  in  the  table  herewith  agree  with  this  assumption.  Attention  should 
be  called  to  the  fact  that  estimates  of  energy  metabohsm  based  on  carbon  dioxide 
production  alone  involve  larger  errors  than  those  based  on  oxygen  consumption 
alone. 


154 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


Energy  Values  of  Oxygen  and  Carbon  Dioxide  at  Different 
Respiratory  Quotients  (Zuntz  and  Schumberg)   {Continued) 


Respiratory 
Quotient 

Calories 

Calories 

Calories 

PER  Liter  of 

PER  Liter  of 

per  Gram  of 

Oxygen 

Carbon  Dioxide 

Carbon  Dioxide 

0.90 

4.924 

5.471 

2.785 

0.91 

4.936 

5-424 

2.761 

0.92 

4.948 

5-378 

2.738 

0.93 

4.960 

5-333 

2.715 

0.94 

4-973 

5.290 

2.693 

0-95 

4.985 

5-247 

2.671 

0.96 

4-997 

5-205 

2.650 

0.97 

5.010 

5.165 

2.629 

0.98 

5.022 

5.124 

2.609 

0.99 

5.034 

5.085 

2.589 

1. 00 

5-047 

5.047 

2.569 

It  is  then  only  necessary  to  determine  the  respiratory  quotient 
and  the  volume  of  oxygen  used  in  order  to  know  the  number 
of  Calories  of  energy  metabolized.  This  is  sometimes  called 
the  method  of  indirect  calorimetry. 

This  method  of  studying  the  total  metabolism  permits  of 
experiments  being  carried  out  very  quickly,  and  is  therefore 
especially  useful  for  the  direct  investigation  of  conditions  which 
affect  metaboHsm  promptly,  such  as  muscular  work  or  the 
eating  of  food.  The  periods  of  observation  cannot  be  very  long, 
but  the  probable  results  for  the  24  hours'  metabohsm  can  be 
estimated  by  the  data  obtained  during  frequent  short  periods 
at  different  times  of  the  day  and  night.  For  a  critical  com- 
parison of  this  method  with  the  Pettenkofer  and  Voit  method 
of  studying  metaboHsm  by  the  determination  of  the  carbon 
balance,  the  reader  is  referred  to  the  discussion  by  Magnus- 
Levy  in  Von  Noorden's  Metabolism  and  Practical  Medicine, 
Vol.  I,  pages  186-198. 

From  the  results  of  many  observations  by  the  Zuntz  method 
Magnus-Levy  estimates  the  minimum  metabolism  of  a  man 
of  average  size  kept  absolutely  motionless  and  fasting  at  1625 


THE  FUEL  VALUE  OF  FOOD  1 55 

Calories  per  day.  Food  barely  sufficient  for  maintenance  would 
increase  this  by  175,  and  such  incidental  muscular  movements 
as  would  ordinarily  be  made  by  a  man  at  rest  in  bed  would  in- 
volve another  200,  making  a  total  of  2000  Calories  as  the  esti- 
mated food  requirement  of  a  man  at  rest  with  a  maintenance  diet. 
Magnus-Levy  further  estimates  that  the  man,  if  doing  no  work 
(in  the  ordinary  sense),  but  allowed  to  move  about  the  room  in- 
stead of  remaining  in  bed,  would  require  2230  Calories  per  day. 

Carbon  and  nitrogen  balance  experiments.  —  From  a  com- 
parison of  the  constituents  of  the  food  consumed  {"  intake  ") 
and  of  the  substances  eHminated  from  the  body  ("  output  "), 
the  material  actually  oxidized  and  the  energy  liberated  in  the 
oxidation  may  be  determined. 

The  intake  is  found  by  weighing  and  analyzing  all  food 
eaten;  the  output  by  collecting  and  determining  the  end 
products  eliminated  through  the  lungs,  the  kidneys,  the  intes- 
tines, and  sometimes  (in  very  exact  experiments)  the  skin.  The 
time  unit  in  experiments  upon  the  intake  and  output  is  almost 
always  24  hours,  the  experimental  day  beginning  preferably  just 
before  breakfast.  The  feces  belonging  to  the  experimental  days 
are  marked,  usually  by  giving  a  small  amount  of  lampblack  with 
the  food  as  in  ordinary  digestion  experiments,  separated  and 
analyzed.  The  end  products  given  off  by  the  lungs  and  kidneys 
during  an  experimental  day  are  taken  as  measuring  the  material 
broken  down  in  the  body  during  the  same  period. 

Some  time  is  of  course  required  for  the  elimination  of  the 
nitrogenous  end  products  through  the  kidneys.  This  un- 
avoidable ''  lag  "  in  the  eHmination  of  nitrogen  may  intro- 
duce an  error  in  determining  the  nitrogen  balance  unless  the 
subject  has  been  kept  for  a  few  days  in  advance  upon  the 
same  diet  which  is  to  be  used  in  the  experiment. 

Assuming  that  the  total  nitrogen  and  carbon  of  the  ab- 
sorbed food  existed  in  the  form  of  protein,  fat,  and  carbo- 
hydrate, and  that  the  amount  of  carbohydrates  in  the  body  is 


156 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


constant  from  day  to  day,  it  is  only  necessary  to  determine  the 
carbon  dioxide  of  the  expired  air  and  the  carbon  and  nitrogen 
of  the  waste  products,  in  order  to  calculate  the  amounts  of 
material  oxidized  and  of  energy  liberated  in  the  body.  Ex- 
periments of  this  sort  have  played  a  most  important  part  in 
the  development  of  our  knowledge  of  nutrition.  The  cal- 
culations are  usually  based  on  the  following  average  analyses 
of  protein  and  body  fat: 

Fat 


Carbon 

Nitrogen 

Hydrogen 

Oxygen 

Sulphur 


76.S 

12 
"•5 


The  following  data  were  obtained  with  a  man  on  ordinary 
mixed  diet: 

Calculation  of  Energy  Metabolism  from  Carbon  and  Nitrogen 
Balance.  Man  of  64  Kilograms  at  Rest  in  Atwater  Respiration 
Apparatus 


Grams  per  Day 

Intake 

Protein 

Fat 

Carbo- 
hydrate 

Nitrogen 

Carbon 

Total  in  food  .     .     . 
Lost  in  digestion 
Absorbed    .... 

94-4 
5-4 
89.0     ♦ 

82.S 

2,-1 

78.8 

289.8 

3-2 

286.6 

15.1 

0.9 

14.2' 

16.2 

16.2 

—  2.0 

239.0 

7-4 
231.6 

Output 

Bv  lunsrs                  

207.^ 

Bv  kidnevs                         

12.2 

Metabolized                      

219.5 

Balance                                       

+  12. 1 

THE  FUEL  VALUE  OF  FOOD  1 57 

A  loss  of  2.0  grams  body  nitrogen  indicates  (2.0  X  6.25  =) 
12.5  grams  body  protein  burned.  Also  there  were  89.0  grams 
absorbed  from  food,  and,  therefore,  in  all  101.5  grams  total 
protein  burned. 

Since  the  respiratory  quotient  showed  that  the  body  was 
in  carbohydrate  equilibrium  at  the  beginning  and  end  of  each 
experimental  day,  i.e.  at  seven  o'clock  each  morning,  it  may 
be  concluded  that  the  amount  of  carbohydrate  burned  was 
J:he  same  as  that  absorbed  from  the  food,  viz.  286.6  grams 
per  day. 

From  the  carbon  balance,  therefore,  w.e  estimate  the  amount 
of  fat  burned  as  follows : 

12.5  grams  body  protein  yield  C12.5  X  53  per 

cent  =  ) 6.6  grams  carbon 

and  there  were  in  the  absorbed  food       .     .     .     .  231.6  grams  carbon 

.'.  total  available  was    .     .     .    " 238.2  grams  carbon 

But  total  catabolized  was  only 219.5  grams  carbon 

.'.  the  body  stored  in  the  form  of  fat 18.7  grams  carbon 

Since  fat  contains  76.5  per  cent  carbon,  i  gram  carbon  =c=  1.307  grams 
fat.    .*.  18.7  grams  carbon  =  24^.4  grams  fat. 

The  body  therefore  absorbed  78.8  grams  fat 
stored  24.4  grams  fat 
burned     54.4  grams  fat 


In  all  the  body  burned  per  day  ' 

101.5  grams  protein,  yielding  •  (101.5  X  4-35*  =  )     442  Calories 
54.4  grams  fat,  yielding  (54.4  X  9-45  *  =  )     5^5  Calories 

286.6  grams  carbohydrate,  yield- 
ing (286.6  X  4.1  *  =  )   1 1 75  Calories 

2132  Calories 

By  means  of  the  carbon  and  nitrogen  balance  Sonden  and 
Tigerstedt  studied  the  energy  metabolism  of  eight  resting  men 
between  nineteen  and  forty-four  years  of  age,  with  results  which 
varied  for  the  different  subjects  from  1853  to  2292  Calories 

*  Here  the  factors  for  fuel  value  are  not  reduced  to  allow  for  loss  in  digestion, 
because  this  loss  has  already  been  deducted  in  computing  the  amount  of  each 
nutrient  actually  absorbed  and  rendered  available. 


158  CHEMISTRY  OF  FOOD  AND  NUTRITION 

per  day.     Many  other  experimenters  have  used  the  same  method 
with  similar  results. 

Calorimeter  experiments.  —  The  most  direct,  and  in  some 
respects  most  convincing,  way  of  ascertaining  the  energy  me- 
tabolism is  by  the  method  of  direct  calorimetry.  This  consists  in 
measuring  the  total  energy  expenditure  of  the  body  as  heat  or 
as  heat  and  mechanical  work  by  confining  the  subject  in  a 
chamber  permitting  of  actual  measurement  of  the  heat  produced. 
It  was  not  until  the  development  of  the  Atwater-Rosa- 
Benedict  respiration  calorimeter  that  complete  and  satisfactory 
data  covering  periods  of  one  to  several  days  were  obtained. 
This  apparatus  consisted  of  an  air-tight  copper  chamber,  sur- 
rounded by  zinc  and  wooden  walls  with  air-spaces  between, 
and  was  large  enough  for  a  man  to  live  in  without  discomfort, 
being  about  7  feet  long,  4  feet  wide,  and  6J  feet  high.  An 
opening  in  the  front  of  the  apparatus,  which  was  sealed  during 
an  experiment,  serves  as  both  door  and  window  and  admits  suf- 
ficient light  for  reading  and  writing.  A  smaller  opening,  having 
tightly  fitting  caps  on  both  ends,  was  used  for  passing  food,  drink, 
excreta,  etc.,  into  and  out  of  the  chamber.  The  chamber 
was  furnished  with  a  folding  bed,  chair,  and  table,  and  was 
ventilated  by  means  of  a  current  of  air  which  passed  usually  at 
the  rate  of  about  2 J  cubic  feet  per  minute.  At  first  this  venti- 
lating air  current  was  maintained  and  measured  by  means  of  a 
specially  constructed  meter  pump  which  also  automatically 
took  samples  of  the  air  for  analysis.  Later  the  apparatus 
was  so  modified  as  to  make  use  of  the  same  air  throughout  an 
experiment,  the  carbon  dioxide  and  water  given  off  by  the  sub- 
ject being  removed  by  circulating  the  air  through  purifying 
vessels,  and  the  oxygen  which  the  subject  uses  being  replaced 
by  adding  weighed  amounts  of  oxygen  to  the  air  current  as 
required.*     By  this  means  it  is  possible  to  carry  out,  in  the 

*  Figure  8  indicates  diagraminatically  the  ventilating  system  as  applied  in  one 
of  the  later  forms  of  apparatus. 


THE  FUEL  VALUE  OF  FOOD 


159 


.^1 s a 


rr-r^ 


TENSION 
EQUALIZER 


0,     INTRODUCED 


L^ 


v> 


1 


r^ 


ABSORBED 


V^ 


H2S 


0. 


C02 

ABSORBED 
POTASH 

LIME 


H2O 
ABSORBED 


H2S  O4 


BLOWER 


Fig.  8.  —  Diagram  of  ventilation  of  respiration  calorimeter.  The  air  is  taken 
out  at  lower  right-hand  corner  and  forced  by  the  blower  through  the  apparatus  for 
absorbing  water  and  carbon  dioxide.  It  returns  to  the  calorimeter  at  the  top. 
Oxygen  can  be  introduced  into  the  chamber  itself  as  need  is  shown  by  the  tension 
equalizer.  Courtesy  of  DV.  F.  G.  Benedict  and  the  Carnegie  Institution  of 
Washington. 


l6o  CHEMISTRY  OF  FOOD  AND  NUTRITION 

calorimeter,  metabolism  experiments  in  which  the  oxygen  and 
hydrogen  as  well  as  the  carbon  and  nitrogen  balances  are 
determined,  and  from  these  data  the  gain  or  loss  of  carbohy- 
drate as  well  as  of  protein  and  fat  can  be  determined. 

The  ventilating  air  current  is  so  regulated  that  it  enters 
and  leaves  the  calorimeter  at  the  same  temperature;  and 
between  the  copper  and  zinc  walls  are  placed  a  large  number 
of  thermo-electric  junctions  connected  with  a  deHcate  gal- 
vanometer by  means  of  which  each  wall  is  tested  every  four 
minutes,  day  and  night,  during  the  progress  of  an  experiment, 
and  the  minute  amounts  of  heat  which  may  pass  to  or  from 
the  calorimeter  through  its  walls  are  quickly  detected  and 
made  to  balance  each  other.  Thus  there  is  no  gain  or  loss  of 
heat  either  through  the  walls  of  the  chamber  or  by  the  venti- 
lating air  current,  and  the  heat  given  off  by  the  subject  can 
leave  only  by  the  means  especially  provided  for  carrying  it 
out  and  measuring  it.  A  part  of  the  heat  hberated  is  carried 
from  the  chamber  in  latent  form  by  the  water  vapor  in  the 
outgoing  air,  which  is  accurately  determined.  The  rest  of 
the  heat  is  brought  away  by  means  of  a  current  of  cold 
water  circulating  through  a  copper  pipe  coiled  near  the  ceiling 
of  the  chamber.  The  quantity  of  water  which  passes  through 
the  pipe  and  the  difference  between  the  temperature  at  which 
it  enters  and  that  at  which  it  leaves  the  coil  are  carefully 
determined  and  show  how  much  heat  is  thus  brought  out  of 
the  chamber. 

In  recent  years  several  different  calorimeters,  based  on  the 
principles  of  the  apparatus  just  described  but  adapted  in  size 
and  shape  to  different  types  of  experimentation,  have  come  into 
use.  Notable  among  these  are  the  "  chair  "  and  the  "  bed  " 
calorimeters,  which  are  so  constructed  as  to  accommodate  a 
subject  in  the  sitting  or  recHning  position  in  comfort  but 
in  a  minimum  of  space;  for  only  by  making  the  calorimeter 
chamber  small  is  it  practicable  to  obtain  a  high  degree  of 


THE  FUEL  VALUE  OF  FOOD 


l6l 


1 62  CHEMISTRY  OF  FOOD  AND   NUTRITION 

accuracy  in  experiments  of  a  few  hours'  duration.  Figures  9, 
10,  and  II  show  sectional  diagrams  of  the  original  calorimeter 
chamber  and  of  the  more  recent  chair  and  bed  calorimeters 
respectively. 

Detailed  and  illustrated  descriptions  of  the  chief  forms  of 
apparatus  now  in  use  may  be  found  in  the  publications  by  Bene- 
dict and  Carpenter,  by  Langworthy  and  Milner,  and  by  Lusk, 
Riche,  and  Soderstrom,  full  references  to  which  are  given  at  the 
end  of  this  chapter. 

By  means  of  the  Atwater-Rosa-Benedict  apparatus  and  its 
various  modifications,  it  has  been  possible  to  measure  the  heat 
production  or  energy  expenditure  of  a  man  for  a  day  or  for  a 
period  of  days  very  accurately.  In  the  original  Atwater-Bene- 
dict  series  it  was  found  that  the  difference  in  results  determined 
by  direct  and  indirect  calorimetry  was  rarely  as  much  as  2 
per  cent,  and  in  the  average  of  45  experiments  covering  a  total 
of  143  days  the  difference  was  only  0.0 1  per  cent.  The  results 
obtained  by  direct  energy  measurements  are  therefore  the 
same  as  those  computed  from  respiration  and  metabohsm  ex- 
periments when  the  technique  is  of  the  best  and  the  experiments 
are  sufficiently  prolonged.  This  agreement  is  in  general  less 
exact  in  individual  experiments  in  proportion  as  the  experi- 
mental periods  are  shortened;  but  the  methods  are  now  so 
highly  developed  that  the  results  of  direct  and  indirect  calo- 
rimetry are  considered  practically  interchangeable  even  for 
experiments  of  a  few  hours'  duration.  In  1913  Armsby  com- 
piled the  following  summary  of  experiments  both  upon  men, 
dogs,  and  cattle  which  had  been  pubHshed  up  to  that  time.  It 
will  be  seen  that  the  difference  between  the  total  heat  produc- 
tion as  computed  and  as  directly  measured  is  only  one  fourth 
of  one  per  cent,  or  quite  within  the  limits  of  accuracy  of  ex- 
perimental methods  of  this  sort. 


Scale  :   I     Meter. 


Fig.  io.  —  Horizontal  cross-section  of  chair  calorimeter,  showing  cross-section  of 
copper  wall  at  A ,  zinc  wall  at  B,  hair-felt  at  E,  and  asbestos  outer  wall  at  F ;  also 
cross-section  of  all  upright  channels  in  the  steel  construction.  At  the  right  is  the 
location  of  the  ingoing  and  outgoing  water  and  the  thermometers.  At  C  is  shown 
the  food  aperture,  and  Z>  is  a  gasket  separating  the  two  parts.  The  ingoing  and 
outcoming  air-pipes  are  shown  at  the  right  inside  the  copper  wall.  The  telephone 
is  shown  at  the  left,  and  in  the  center  of  the  drawing  is  the  chair  with  its  foot-rest,  G. 
In  dotted  line  is  shown  the  opening  where  the  man  enters.  Courtesy  of  Dr.  F.  G. 
Benedict  and  the  Carnegie  Institution  of  Washington. 


164 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


Experimenter 

Total 

Number 

OF 

Days 

Total 
Computed 

Heat 

Production 

Calories 

Total  Observed 

Heat 

Production 

Calories 

Percentage 
Difference 

Rubner    ...... 

Laulanie 

Atwater  and  Benedict    . 
Benedict  and  Milncr      . 

Benedict 

Armsby  and  Fries     .     . 

45 

7 

93 

24 

53 
114 

17,406 

1,865 

249,063 

95,075 
102,078 
976,204 

17,350 

1,859 

248,930 

95,689 
101,336 
980,234 

TO.32 

-  0.31 

—  0.05 
+  0.65 

-0.73 
+  0.41 

336 

1,441,691 

1,445,398 

+  0.26 

As  Armsby  points  out :  "  These  results  may  be  taken  as  dem- 
onstrating that  the  animal  heat  arises  exclusively  from  the 
combustions  in  the  body,  but  they  have  a  much  broader  sig- 
nificance. They  show  that  the  transformations  of  chemical 
energy  into  heat  and  work  in  the  animal  body  take  place  ac- 
cording to  the  same  general  laws  and  with  the  same  equivalencies 
as  in  our  artificial  motors  and  in  Hfeless  matter  generally, 
The  great  law  of  the  conservation  of  energy  rules  in  the 
animal  mechanism,  whether  in  man,  carnivora,  or  herbivora, 
just  as  in  the  engine.  The  body  neither  manufactures  noi 
destroys  energy.  All  that  it  gives  out  it  gets  from  its  food, 
and  all  that  is  supplied  in  its  food  is  sooner  or  later  recovered 
in  some  form." 

Since  the  time  of  Armsby's  compilation  the  agreement  be- 
tween the  observed  and  computed  heat  production  has  beer 
confirmed  in  many  additional  experiments,  and  both  by  the 
same  and  different  experimenters. 

Working  with  the  original  Atwater  calorimeter,  Atwater  anc 
Benedict  conducted  "  rest "  experiments  upon  six  different 
men  who  lived  in  the  calorimeter  as  quietly  as  was  feasible  foi 
days  at  a  time,  taking  as  a  rule  but  little  more  exercise  thar 
was  involved  in  dressing  and  undressing,  folding  and  unfolding 


THE  FUEL  VALUE  OF  FOOD 


i6s 


the  bed,  table,  and  chair,  taking  samples  and  observations 
pertaining  to  the  experiment,  writing,  etc.,  in  short,  the  life  of 
a  healthy  man,  confined  to  one  small  room. 

The  average  daily  metaboUsm  of  each  of  the  subjects  was  as 
follows : 


Subject 


Age 
Years 


Weight 
Average 


Number  of 
Experi- 
ments 


Total  Ex- 
perimental 
Days 


Calories 
PER  Day 


E.  O.       . 
A.  W.  S. 


J.  F.  S. 


J.  C.  W. 


H.  F. 


B.  F.  D. 


Mean  of  individual 
averages      .     .     . 


31-34 
22-25 

29 

21 

54 

23 


70  K. 
(154  lb.) 

70  K. 
(154  lb.) 

65  K. 
(143  lb.) 

76  K. 
(168  lb.) 

70  K. 
(154  lb.) 

67  K. 
(147  lb.) 


42 

9 
12 

4 
3 
3 


2283 
2337 
2133 
2397 
1904 
2228 


2213 


Extreme  deviations  from  the  mean,  +  184  to  —  309  Calories, 

or  +  8.4  to  —  14  per  cent. 

Omitting  the  results  obtained  with  the  one  subject  who 
was  considerably  older  than  the  others,  the  figures  become  as 
follows : 

Mean  of  individual  averages,     2277  Calories. 
Extreme  deviations  from  mean,  +  120  to  —  144.  Calories, 
or  H-   5.2  to  —  6.3  per  cent. 

Deviations  in  body  weight,  -\-   8.7  to  —  7.1  per  cent. 

The  subject  "  H.  F.,"  aged  fifty-four,  who  beHeved  that 
he  consumed  only  half  the  usual  amount  of  food,  had  a  food 
requirement  about  15  per  cent  less  than  that  of  the  younger 


1 66  CHEMISTRY  OF  FOOD  AND   NUTRITION 

men  averaging  about  the  same  weight.  The  five  younger  men 
varied  in  age  from  twenty-one  to  thirty-four  years,  were  natives 
of  three  different  countries,  and  had  been  accustomed  to  very 
different  dietary  habits  and  modes  of  Hfe,  yet  they  differed  less 
in  energy  requirements  than  in  body  weight. 

Summary  of  the  Evidence  Obtained  by  the  Different  Methods 

A  general  view  of  the  results  obtained  by  all  four  of  the 
methods  described  shows  them  to  be  strikingly  consistent  and 
leads  to  the  conclusion  that  the  food  requirements  of  a  young 
to  middle-aged  man  of  average  size,  without  muscular  work, 
eating  a  mixed  diet  sufficient  to  meet  his  need,  approximates 
2000  Calories  per  day,  and  that  such  muscular  activity  as  is 
incidental  to  very  quiet  living  indoors  may  be  expected  to  raise 
this  requirement  to  about  2200  Calories  per  day. 

Lusk  summarizes  the  mean  energy  requirement  of  an  average 
sized  man  in  somewhat  more  precise  terms  as  follows : 

Absolute  rest  in  bed  without  food 1680  Calories 

Absolute  rest  in  bed  with  food 1840  Calories 

Rest  in  bed,  8  hours,  sitting  in  chair  16  hours, 

with  food 2168  Calories 

The  very  close  agreement  in  results  reached  by  many  inde- 
pendent investigators,  using  four  distinct  methods  of  study, 
must  be  taken  as  establishing  the  approximate  average  food 
requirement  of  a  man  at  rest  beyond  any  reasonable  doubt. 

Significance  of  Basal  Energy  Metabolism 

On  account  of  the  great  importance  of  the  fundamental 
energy  expenditure  both  for  the  study  of  normal  nutrition, 
and  as  a  basis  for  comparison  in  the  investigation  of  disease, 
the  experiments  above  described  have  been  followed  by  others 


THE  FUEL  VALUE  OF  FOOD 


167 


designed  to  establish  with  even  greater  exactness  the  *'  basal 
metaboHsm  "  which  goes  on  when  the  direct  effect  of  food  is 
excluded  and  when  muscular  activity  is  suppressed  as  com- 


pletely as  possible.  Experiments  of  this  latter  type  must  neces- 
sarily be  carried  out  in  shorter  periods  than  were  used  in  the 
Atwater  investigations  described  above.     Being  shorter,  they 


1 68  CHEMISTRY  OF  FOOD  AND  NUTRITION 

can  be  more  frequently  repeated  and  more  readily  extended  to 
cover  a  larger  number  of  individuals. 

Data  obtained  in  such  studies  of  "  basal  metabolism  "  will 
be  cited  later  in  connection  with  the  study  of  the  various  con- 
ditions which  influence  the  energy  metaboUsm  and  total  food 
•requirement. 

A  systematic  analysis  of  the  maintenance  requirement  of 
the  body  with  reference  to  its  principal  functions  has  not  yet 
been  made,  but  results  obtained  by  Armsby,  Atwater,  Benedict, 
Lusk,  Magnus-Levy,  Rubner,  Zuntz,  and  others  indicate  that 
in  the  healthy  adult  the  expenditure  of  energy  when  at  rest 
and  no  longer  influenced  by  the  direct  effect  of  food  ("  basal 
energy  metabolism  ")  may  be  attributed  in  part,  perhaps  up 
to  one  tenth,  to  the  work  of  the  heart  in  maintaining  the  cir- 
culation ;  from  one  tenth  to  two  tenths  to  the  muscular  work 
of  respiration ;  from  one  third  to  one  half,  or  perhaps  even  more, 
to  the  maintenance  of  muscular  tonus  (tone,  tension,  elasticity) ; 
and  an  unknown  fraction  to  other  forms  of  internal  work. 

REFERENCES 

Armsby.     Principles  of  Animal  Nutrition,  Chapters  7  to  10. 

Armsby.  Food  as  Body  Fuel.  Pennsylvania  Agricultural  Experiment 
Station,  Bulledn  126. 

Atwater.  Methods  and  Results  of  Investigations  on  the  Chemistry  and 
Economy  of  Food.  Bull.  21,  Office  of  Experiment  Stations,  U.  S. 
Dept.  Agriculture  (1895). 

Atwater.  Neue  Versuche  iiber  Stoff-  und  Kraft-wechsel.  Ergebnisse 
der  Physiologic,  Vol.  3  (1904). 

Atwater  and  Benedict.    A  Respiration    Calorimeter  with  Appliances  * 
for  the  Direct  Determinarion  of  Oxygen.     Publication  No.  42,  Car- 
negie Institution  of  Washington  (1905). 

Atwater  and  Snell.  A  Bomb  Calorimeter  and  Method  of  its  Use.  Jour- 
nal of  the  American  Chemical  Society,  Vol.  25,  page  659  (1903). 

Benedict.  An  Apparatus  for  Studying  the  Respiratory  Exchange.  Amer- 
ican Journal  of  Physiology,  Vol.  24,  pages  345-374  (1909). 

Benedict  and  Carpenter.    Respiration  Calorimeters  for  Studying  the 


THE  FUEL  VALUE  OF  FOOD  169 

Respiratory  Exchange  and  Energy  Transformations  in  Man.  Car- 
negie Institution  of  Washington,  Publication  No.  123. 

Carpenter.  A  Comparison  of  Methods  for  Determining  the  Respiratory 
Exchange  of  Man.  Carnegie  Institution  of  Washington,  Publication 
No.  216. 

Langworthy  and  Milner.  An  Improved  Respiration  Calorimeter  for 
Use  in  Experiments  with  Man.  Journal  of  Agricultural  Research, 
Vol:  5,  page  299. 

Lusk.     Elements  of  the  Science  of  Nutrition. 

Lusk,  Riche,  and  Soderstrom.  a  Respiration  Calorimeter  for  the  Study 
of  Disease.     Archives  of  Internal  Medicine^  Vol.  15,  pages  793,  805. 

Mathews.     Physiological  Chemistry,  Chapter  VI. 

Rubner.     Die  Gesetze  der  Energieverbrauch  bei  dcr  Ernahrung. 

Von  Noorden.    Metabohsm  and  Practical  Medicine. 


CHAPTER  VII 

CONDITIONS      GOVERNING     ENERGY     METABOLISM 
AND    TOTAL    FOOD    REQUIREMENT 

Activity,  age,  and  size  are  the  most  important  factors  af- 
fecting the  total  food  requirement  of  the  body,  but  several 
other  conditions,  such  as  bodily  constitution  and  environment, 
may  have  measurable  influence.  Since  the  food  requirement  of 
the  adult  is  more  accurately  known  than  that  of  the  growing 
organism,  it  will  be  best  to  consider  the  conditions  affecting 
the  energy  metabolism  of  the  adult  first  and  the  demands  of 
growth  later. 

Basal  Metabolism  of  the  Adult 

The  basal  rate  of  energy  metabolism,  as  shown  by  the  heat 
production  (determined  either  by  direct  or  indirect  calorimetry) 
at  complete  rest  and  at  a  sufficiently  long  time  after  the  last 
meal  to  eliminate  the  direct  effects  of  food,  has  now  been  studied 
in  considerable  detail.  In  the  healthy  adult  this  basal  metab- 
olism depends  chiefly  upon  the  size,  shape,  and  composition  of 
the  body  and  the  activity  of  certain  internal  processes.  It 
may  or  may  not  be  appreciably  influenced  by  the  temperature 
of  the  surroundings. 

Influence  of  the  size,  shape,  and  composition  of  the  body.  — 
For  different  adults  of  the  same  species  the  energy  metaboHsm 
and  therefore  the  total  food  requirement  as  a  rule  increases 
with  the  size,  but  not  to  the  same  extent  that  the  body  weight 
increases ;   so  that  the  requirement,  though  greater  in  absolute 

170 


CONDITIONS   GOVERNING  ENERGY  METABOLISM        1 71 

amount,  is  less  per  unit  of  body  weight  in  the  larger  individual 
than  in  the  smaller.  The  energy  metabolism  increases  in  pro- 
portion to  the  surface  rather  than  the  weight.  Thus,  Rubner 
collected  the  following  data  from  experiments  upon  seven  dif- 
ferent dogs,  all  full  grown  but  differing  greatly  in  size. 


Heat  Production  in  Calories  per  Day 

Body  Weight 
Kilograms 

No. 

Total 

Per  kilogram  of 

Per  square  meter 

body  weight 

of  body  surface 

I 

3-IO 

273.6 

88.25 

1214 

II 

6.44 

417.3 

64.79 

II20 

III 

9.51 

619.7 

65.16 

1 183 

IV 

17.70 

817.7 

46.20 

1097 

V 

19.20 

880.7 

45.87 

1207 

VI 

23.71 

970.0 

40.91      . 

III2 

VII 

30.66 

1 1 24.0 

36.66 

1046 

Here  the  heat  production  in  calories  per  kilogram  was  over 
twice  as  great  in  the  smallest  as  in  the  largest  dog,  but  the  total 
metaboHsm  was  nearly  proportional  to  the  surface  area  through- 
out. 

That  the  relationship  of  energy  metabolism  to  body  surface 
is  not  due  simply  to  loss  of  heat  through  the  cooHng  effect  of 
the  environment  will  be  apparent  from  the  observations  upon 
the  regulation  of  body  temperature. 

Armsby,  in  his  Principles  of  Animal  Nutrition^  quotes  the 
explanation  offered  by  von  Hosslin  —  that  the  internal  work 
and  the  consequent  heat  production  in  the  body  are  substantially 
proportional  to  the  two  thirds  power  of  its  volume,  and*  since 
the  external  surface  bears  the  same  ratio  to  the  volume,  a 
proportionahty  necessarily  exists  between  heat  production  and 
surface. 

Largely  as  the  result  of  Rubner 's  work,  it  became  customary 
to  express  energy  requirements  in  terms  of  surface;    but,  on 


172  CHEMISTRY  OF  FOOD  AND   NUTRITION 

account  of  the  difficulties  involved  in  actual  measurements, 
the  surface  was  customarily  computed  from  the  weight,  usually 
by  Meeh's  formula  S  =  W^XC  or  5  =  i2.3^'|P,  in  which  5 
represents  the  surface  and  W  the  weight,  the  constant  12.3 
having  been  found  by  Meeh  in  a  series  of  measurements  of 
men. 

Benedict  found  that  the  basal  metabolism  of  normal  men 
and  women  per  unit  of  surface  as  computed  from  the  weight  by 
the  Meeh  formula  is  by  no  means  constant,  varying  from  29  to 
40  Calories  per  square  meter  per  hour  among  89  men,  and 
from  26  to  38  Calories  per  square  meter  per  hour  among  68 
women. 

Recently  DuBois  and  DuBois  have  made  a  new  series  of 
measurements  of  body  surface  in  which  they  find  that  Meeh's 
formula  gives  results  which  are  much  too  high,  probably  because 
Meeh's  measurements  were  made  on  thin  men.  Tabulating 
the  results  of  other  measurements  with  their  own,  they  find 
that  among  the  20  cases  of  direct  measurements  of  body  surface 
which  had  been  reported  up  to  19 15,  the  errors  in  results  com- 
puted by  Meeh's  formula  range  from  —7  to  +36  per  cent. 
Differently  stated,  if  the  principle  of  Meeh's  formula  be  em- 
ployed it  would  be  necessary  to  vary  the  "  constant  "  from  9.06 
to  13.17  in  order  to  express  the  relationships  of  weight  and 
surface  actually  found  among  these  20  individuals. 

The  errors  involved  in  computing  the  surface  from  the  weight 
alone  are  therefore  much  greater  than  were  formerly  sup- 
posed. DuBois  and  DuBois  have  devised  two  new  methods 
by  which  the  surface  may  be  computed  with  much  greater  ac- 
curacy: (i)  from  a  series  of  nineteen  measurements  of  differ- 
ent parts  of  the  body,  the  surface  of  each  part  being  computed 
and  the  results  added  together  ("  linear  formula  "),  and  (2)  a 
"  height-weight  formula  "  which  these  authors  have  derived 
mathematically  from  the  data  of  all  available  measurements  of 
height,  weight,  and  surface. 


CONDITIONS   GOVERNING  ENERGY  METABOLISM       173 
The  height-weight  formula  may  be  written  thus : 

^=  ^0.425  xZf0.725xC 

or  in  the  form : 

Log  A  =  (Log  WX  0.425)  +  (Log  H  X  0.725)  +  1.8564 
in  either  of  which 

A  =  Surface  area  in  square  centimeters 

H  =  Height  in  centimeters 

W  =  Weight  in  kilograms 

C  =  A  constant  (71.84) 

In  connection  with  this  formula  the  authors  give  also  a  chart  * 
from  which  the  approximate  surface  area  may  be  obtained  at 
a  glance  if  height  and  weight  are  known.  The  data  given  in 
the  accompanying  table  have  been  taken  from  the  DuBois 
chart. 

Table  Showing  Surface  Area  in  Square  Meters  for  Different 
Heights  and  Weights  according  to  the  Height-Weight  Formula 
OF  DuBois  AND  DuBois 


Height 

Weight  in  Kilograms 

IN  Centi- 
meters 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

75 

80 

85 

90 

95 

100 

lOS 

200 

1.84 

1.91 

1.97 

2.03 

2.09 

2.15 

2.21 

2.26 

2.31 

2.36 

2.41 

195 

1-73 

1.80 

1.87 

1-93 

1.99 

2.05 

2. II 

2.17 

2.22 

2.27 

2.32 

2.37 

190 

1.56 

1.63 

1.70 

1.77 

1.84 

1.90 

1.96 

2.02 

2.08 

2.13 

2.18 

2.23 

2.28 

2.33 

i8s 

1-53 

1.60 

1.67 

1.74 

1.80 

1.86 

1.92 

1.98 

2.04 

2.09 

2.14 

2.19 

2.24 

2.29 

180 

1.49 

1-57 

1.64 

1. 71 

1.77 

1.83 

1.89 

1-95 

2.00 

2.05 

2.10 

2.15 

2.20 

2.2s 

175 

1. 19 

1.28 

1.36 

1.46 

1-53 

1.60 

1.67 

1-73 

1.79 

1.85 

1.91 

1.96 

2.01 

2.06 

2. II 

2.16 

2.21 

170 

1. 17 

1.26 

1-34 

1-43 

1.50 

1-57 

1.63 

1.69 

1-75 

1.81 

1.86 

1.91 

1.96 

2.01 

2.06 

2. II 

i6s 

1.14 

1.23 

1-31 

1.40 

1.47 

1-54 

1.60 

1.66 

1.72 

1.78 

1.83 

1.88 

1-93 

1.98 

2.03 

2.07 

160 

1. 12 

1. 21 

1.29 

1.37 

1.44 

1.50 

1,56 

1.62, 

1.68 

1-73 

1.78 

1.83 

1.88 

1-93 

1.98 

ISS 

1.09 

1. 18 

1.26 

1-33 

1.40 

1.46 

1.52 

1.58 

1.64 

1.69 

1.74 

1.79 

1.84 

1.89 

150 

1.06 

1. 15 

1.23 

1.30 

1.36 

1.42 

1.48 

1-54 

1.60 

1.65 

1.70 

1-75 

1.80 

14s 

1.03 

1. 12 

1.20 

1.27 

1-33 

1-39 

1-45 

I-5I 

1.56 

1.61 

1.66 

1. 71 

140 

1. 00 

1.09 

1. 17 

1.24 

1.30 

1.36 

1.42 

1.47 

1-52 

1-57 

I3S 

0.97 

1.06 

1. 14 

1.20 

1.26 

1.32 

1.38 

1-43 

1.48 

130 

3-95 

1.04 

I. II 

1. 17 

1.23 

1.29 

1-35 

1.40 

125 

3-93 

1. 01 

1.08 

1. 14 

1.20 

1.26 

I-3I 

1.36 

120 

0.91 

0.98 

1.04 

1. 10 

1. 16 

1.22 

1.27 

*  Reproduction  of  the  chart  may  be  found  on  page 
Lusk's  Science  of  Nutrition. 


26  of  the  third  edition  of 


174  CHEMISTRY  OF  FOOD  AND  NUTRITION 

On  applying  the  "  height- weight  formula  "  to  the  recorded 
energy  metabolism  of  the  large  number  of  men  studied  in  Bene- 
dict's laboratory,  as  well  as  in  his  own,  DuBois  finds  that  all 
the  data  for  men  under  50  years  of  age  are  within  15  per  cent 
of  the  average  basal  heat  production  of  39.7  Calories  per  hour 
per  square  meter  of  surface  area  properly  computed,  and  that 
86  per  cent  of  all  the  cases  are  within  10  per  cent  of  the  average. 
Means,  using  the  more  accurate  "  Hnear  formula,"  finds  all  of 
his  16  normal  cases  (9  men  and  7  women)  and  also  most  of  his 
obesity  cases  to  fall  within  DuBois'  "  normal  limits "  {i.e. 
within  10  per  cent  of  DuBois'  average  of  39.7  Calories  per  square 
meter  per  hour).  DuBois  ^  believes  that  one  may  *'  feel  cer- 
tain that  with  men  between  the  ages  of  20  and  50  the  (basal) 
metabolism  of  each  individual  is  proportional  to  his  surface 
area  whether  he  be  short  or  tall,  fat  or  thin." 

Differences  of  build  (shape  of  body)  are  associated  not  only 
with  varying  ratios  of  weight  to  surface  but  also  with  differ- 
ences of  fatness,  i.e.  of  body  composition.  The  thin  man,  be- 
sides having  a  greater  surface  in  proportion  to  his  weight, 
differs  also  from  the  stout  man  in  that  a  larger  percentage  of  his 
body  is  actual  protoplasm.  Since  the  metaboHsm  of  the  body 
depends  more  upon  its  weight  of  protoplasm  (active  tissue)  than 
upon  its  total  weight,  we  have  here  an  important  reason  for 
believing  that  the  food  requirement  will  be  greater  in  a  tall, 
thin  man  than  in  a  shorter  and  fatter  man  of  the  same  weight. 

Von  Noorden  tested  this  question  by  observing  the  metab- 
olism (for  one  day  without  food)  of  two  men  of  different  build 
but  nearly  the  same  weight.  The  results  were  as  follows: 
ist  man,  thin  and  muscular,  weight  71. i  kilograms  —  2392 
Calories  =  33.6  Calories  per  kilogram;  2d  man,  stout,  weight 
73.6  kilograms  —  2136  Calories  =  29.0  Calories  per  kilogram. 
These  two  men  had  nearly  the  same  weight  but  differed  in 
height,  in  body  composition,  and  in  energy  expenditure. 

1  American  Journal  of  the  Medical  Sciences,  June,  1916,  page  786. 


CONDITIONS   GOVERNING  ENERGY  METABOLISM       175 

Even  with  the  same  height  and  weight  there  may  be  differ- 
ences in  the  composition  of  the  body.  Thus  a  man  of  average 
height  and  weight  but  large-boned  and  loosely  built  will  be  of 
less  than  average  fatness;  a  man  of  the  same  height  but  less 
broad-shouldered  must  be  somewhat  fatter  in  order  to  weigh 
the  same.  Hence  equality  of  height  and  weight  does  not  neces- 
sarily imply  the  same  shape  and  composition  of  body.  Bene- 
dict finds  among  normal  adults  of  like  height  and  weight  the 
basal  metabohsm  of  athletes  about  five  per  cent  higher,  and 
that  of  women  about  five  per  cent  lower,  than  that  of  average 
non-athletic  men.  He  attributes  these  divergencies  to  differ- 
ences in  body  composition,  holding  that  women  have  some- 
what more  fat,  and  athletes  somewhat  less,  than  non-athletic 
men  of  the  same  weight  and  height. 

Internal  activities.  —  The  work  of  maintaining  the  respiration 
and  circulation  evidently  involves  a  continual  expenditure  of 
energy.  It  is  clear  too  that  deep  and  rapid  breathing  or  vigor- 
ous heart  action  must  involve  an  increased  activity  of  the 
muscles  concerned.  But  it  is  not  always  clear  to  what  extent 
increased  respiratory  and  heart  action  are  a  cause  and  to  what 
extent  they  are  an  effect  of  increased  energy  metabolism.  Thus 
MurHn  and  Greer  ^  emphasize  the  close  relationship  of  the 
heart  to  the  requirements  of  the  tissues  for  energy  in  that  the 
energy  metabolism  is  immediately  dependent  upon  oxygen  sup- 
ply. Since  but  little  available  oxygen  can  be  stored  in  the  living 
substance,  ''  the  response  of  the  heart  to  variations  in  the 
(energy)  requirement  must  be  immediate  and,  within  very 
narrow  limits  of  time,  proportional  to  this  requirement." 
And  Benedict  states  that : 

If  subject  A,  in  a  resting  post-absorptive  condition,  has  on 
a  given  day  a  pulse  rate  of  70  per  minute,  and  on  a  subsequent 
day  under  exactly  the  same  conditions  has  a  pulse  rate  of  60  per 
minute,  it  may  be  asserted  with  every  degree  of  confidence  that 

1  American  Journal  of  Physiology,  Vol.  33,  page  253. 


176 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


the  metabolism  on  the  second  day  will  be  perceptibly,  indeed 
measurably,  lower  than  the  first. 

A  large  factor  in  basal  metabolism  is  the  maintenance  of 
muscular  tension  or  tone.  That  every  living  muscle  is  always 
in  a  state  of  tension  is  evident  from  the  fact  that  it  gapes 
open  if  cut.  It  is  equally  evident  that  the  degree  of  tension 
(and  therefore  the  expenditure  of  energy  required  to  maintain 
it)  varies  greatly  in  different  individuals  under  similar  conditions 
and  in  the  same  individual  under  different  conditions.  The 
differences  observed  by  Atwater  and  Benedict  between  the 
metabolism  of  the  sleeping  hours  and  that  of  the  hours  spent 
sitting  up  without  muscular  movement  (65  and  100  Calories 
respectively)  are  largely  due  to  the  more  complete  relaxation 
of  the  muscles  during  sleep.  Thus  there  is  in  the  *'  resting  " 
muscle  a  continual  expenditure  of  energy  which  first  takes  the 
form  of  muscular  tension,  or  tone,  but  ultimately  appears  as 
heat,  so  that  the  heat  production,  or  energy  metabolism,  of 
the  body  at  rest  depends  to  a  considerable  extent  upon  the 
degree  of  tension  which  still  persists  in  the  muscles. 

Benedict  and  Carpenter  report  the  following  figures  in 
Calories  per  hour,  for  the  energy  metaboHsm  during  sleep 
(i  A.M.  to  7  A.M.)  following  different  conditions  of  activity 
and  showing  the  after  effects  of  work  upon  muscular  tension 
during  rest: 

Energy  Metabolism  during  Sleep  —  Calories  per  Hour 


Subject 

Sleep  after 
Rest 

Sleep  after 

Moderate 

Work 

Sleep  after 
Severe 
Work 

Sleep  after 

Very   Severe 

Work 

E.  0 

J.F.S 

J.  C.W 

B.  F.  D 

A.L.L 

69.3 
60,4 
77.2 
69.8 
•       78.3 

74-8 
65.3 

83.1 
83.3 
83.7 

97-9 

CONDITIONS  GOVERNING  ENERGY  METABOLISM       177 

Benedict  also  finds  that  even  under  the  most  quiet  conditions 
a  higher  tension  gradually  develops  during  the  waking  hours. 
A  fasting  man  metabolized  when  lying  at  complete  rest  14  per 
cent  more  in  the  morning  than  when  sound  asleep  at  night, 
and  22  per  cent  more  in  the  late  afternoon  than  when  asleep. 

Does  mental  work  influence  energy  metabolism?  —  In  any 
consideration  of  this  question  it  is  important  to  distinguish 
sharply  between  the  nervous  control  of  muscular  conditions 
and  the  metabolism  of  the  brain  and  nerve  substance  itself. 
As  emphasized  particularly  by  Mathews,  the  brain  receives  a 
copious  blood  supply,  and  the  blood  coming  to  the  brain  is 
arterial^  while  that  leaving  the  brain  is  venous,  indicating  that 
considerable  oxidative  metabolism  occurs  in  brain  tissue. 
Recently  also  Tashiro  has  shown  that  the  carbon  dioxide  pro- 
duction of  nerve  fiber  is  increased  when  the  nerve  is  stimulated 
to  activity.  But  since  the  entire  weight  of  brain  and  nerve 
substance  constitutes  only  about  2  per  cent  of  the  body  weight, 
it  remains  questionable  whether,  even  if  its  metabohsm  in- 
creases with  "  mental  activity,"  the  increase  would  be  ap- 
preciable in  measurements  of  the  energy  expenditure  of  the 
body  as  a  whole.  Probably  the  best-controlled  experiments 
upon  this  problem,  certainly  the  ones  affording  most  accurate 
measurement  of  the  energy  expenditure,  are  those  of  Benedict 
and  Carpenter,  in  which  a  number  of  college  students  were  given 
course  examinations  in  the  respiration  calorimeter  and  their 
energy  metabolism  during  the  three-hour  period  covered  by 
the  examination  was  compared  with  that  during  the  same 
period  on  another  day  when  the  student  sat  in  the  calorimeter 
at  rest.  In  some  individuals  the  metabohsm  was  higher  during 
the  examination  period,  while  in  others  it  was  lower  —  results 
much  more  likely  due  to  involuntary  increase  or  decrease  of 
muscular  tension  than  to  altered  metabohsm  of  the  brain 
tissue.  In  the  average  of  the  entire  series  of  experiments  tliere 
appeared  a   slight  increase  of  oxygen  consumption,   carbon 

N 


178  CHEMISTRY  OF  FOOD  AND   NUTRITION 

dioxide  output,  and  heat  production  during  the  examination, 
but  the  increase  was  so  small  and  the  exceptions  so  numerous 
that  the  investigators  were  not  willing  to  conclude  from  their 
results  that  mental  work  has  any  positive  effect  upon  the  total 
metabolism,  but  rather  infer  the  opposite. 

Apparently  we  must  conclude  that  such  changes  in  energy 
metabolism  as  may  result  from  differences  in  activity  of  the 
brain  and  nerves  involved  in  the  performance  of  mental  work 
are  so  small,  in  comparison  with  the  energy  exchanges  always 
going  on  in  the  muscles,  that  the  former  are  quite  obscured 
by  the  unavoidable  fluctuations  of  the  latter,  and  so  play  no 
measurable  part  in  determining  the  total  food  requirement  of 
the  body. 

Internal  secretions^  notably  that  of  the  thyroid  gland,  may 
exert  a  significant  influence  upon  energy  metabolism  through 
augmenting  the  heart  action  and  respiration  rate,  probably 
also  through  heightened  muscular  tension,  and  possibly  in 
other  ways.  Lusk  says :  "  With  the  possession  of  such  a  gland 
as  the  thyroid,  whose  suppression  may  diminish  metabolism 
twenty  per  cent  and  whose  stimulation  may  increase  it  100  per 
cent,  it  is  truly  strange  that  the  normal  person  should  have  a 
basal  metabolism  so  regulated  as  to  correspond  to  a  definite 
heat  loss  per  square  meter  of  body  surface."  If,  however, 
the  thyroid  gland  is  conspicuously  over-  or  under-developed 
in  size  or  activity  the  condition  is  regarded  as  a  departure 
from  health  (goiter,  myxedema) ;  the  effect  of  these  and  some 
other  diseases  upon  energy  metabolism  has  been  summarized 
recently  by  DuBois  ^  as  follows : 

"  Basal  metabolism  is  higher  than  normal  in  exophthalmic 
goiter,  in  fever,  in  lymphatic  leukemia  and  pernicious  anemia, 
in  severe  cardiac  disease,  and  in  some  cases  of  severe  diabetes 
and  cancer.  It  is  lower  than  normal  in  cretinism  and  myxedema, 
in  old  age,  in  some  wasting  diseases,  and  perhaps  in  some  cases 

1  Archives  oj  Internal  Medicine,  Vol.  17,  page  916  (1916). 


CONDITIONS   GOVERNING  ENERGY  METABOLISM       179 

of  obesity."  ^'  Diseases  of  the  ductless  glands  other  than  thy- 
roid show  in  some  cases  an  increase,  in  some  a  decrease;  but 
these  are  comparatively  small." 

Benedict  ^  also  holds,  in  opposition  to  some  other  authorities, 
that  "  when  a  carbohydrate-free  diet  is  eaten  an  acidosis  is 
developed  which  distinctly  increases  the  cellular  activity  and 
results  in  a  very  noticeable  increase  in  the  basal  metaboHsm." 

In  a  recent  general  review  of  the  factors  affecting  normal 
basal  metabolism  Benedict ^  concludes  "that  the  basal  metab- 
olism of  an  individual  is  a  function,  first,  of  the  total  mass  of 
active  protoplasmic  tissue,  and,  second,  of  the  stimulus  to  cellu- 
lar activity  existing  at  the  time  the  measurement  of  the  metab- 
olism was  made."  And  that:  "Perhaps  the  most  striking- 
factors  causing  variations  in  the  stimulus  to  cellular  activity 
are  age,  sleep,  prolonged  fasting,  character  of  the  diet,  and 
the  after  effect  of  severe  muscular  work." 

Influence  of  Muscular  Work  upon  Metabolism  and  Food 
Requirement 

Muscular  work  is  much  the  most  important  of  the  factors 
which  raise  the  food  requirements  of  adults  above  the  basal  rate 
necessary  for  mere  maintenance. 

Accurate  measurements  by  means  of  the  calorimeter  have 
shown  that  the  average  total  metabolism  of  a  man  sitting  still 
is  about  100  Calories  per  hour;  while  the  same  man  working 
actively  increases  his  metabolism  up  to  about  300  Calories  per 
hour ;  and  a  well-trained  man  working  at  about  his  maximum 
capacity  metabolizes  material  enough  to  Hberate  600  Calories 
per  hour,  i.e.  his  metabolism  may  be  six  times  as  active  during 
the  hours  actually  spent  in  such  work  as  when  he  is  at  rest. 
If  during  24  hours  a  man  works  as  hard  as  this  for  8  hours  and 
spends  2  hours  in  such  Hght  exercise  as  going  to  and  from  work, 

^  Journal  of  Biological  Chemistry,  Vol.  18,  page  141  (July,  1914). 

2  Proceedings  of  the  National  Academy  of  Sciences,  Vol.  i,  pages  105-109. 


l8o  CHEMISTRY  OF  FOOD  AND  NUTRITION 

his  food  requirement  for  the  day  will  be  somewhat  over  6000 
Calories,  or  three  times  the  maintenance  requirement.  Thus, 
work  may  increase  the  day's  metaboHsm  as  much  as  200  per 
cent,  whereas  liberal  feeding  at  the  end  of  a  fast  was  found  to 
increase  the  metabohsm  only  22.5  per  cent,  or  one  ninth  as 
much.  Only  a  few  exceptional  occupations,  such  as  that  of 
lumbermen,  for  example,  involve  such  heavy  work  as  to  cause 
a  metabolism  of  6000  Calories  per  day.  More  often  the  man 
who  works  8  hours  a  day  at  manual  labor  will  increase  his 
metabolism  by  1000  to  2000  Calories  above  what  is  needed  for 
maintenance  at  rest,  making  his  total  food  requirement  3000  to 
4000  Calories. 

Voit  estimated  the  food  requirement  of  a  "  moderate  worker  '* 
at  about  3050  Calories ;  and  Atwater,  in  adapting  this  standard 
to  American  conditions,  increased  the  allowance  to  3400-3500 
Calories  in  the  belief  that  the  American  works  more  rapidly 
and  therefore  with  a  greater  expenditure  of  energy.  The  mis- 
take is  often  made  of  supposing  that  these  estimates  were  in- 
tended for  every  one  who  leads  an  active  life,  whereas  they  really 
contemplate  a  long  day  of  manual  labor,  for  Voit's  definition 
of  "  moderate  worker  "  was  a  man  laboring  9  or  10  hours  a  day 
at  an  occupation  such  as  that  of  a  carpenter,  mason,  or  joiner. 

The  amount  of  energy  spent  during  24  hours  by  a  sedentary 
worker  will  depend  not  only  upon  the  number  of  hours  which 
he  devotes  to  exercise,  but  especially  upon  the  kind  of  exercise 
chosen.  Lusk  estimates  that  an  average-sized  man  sleeping 
8  hours,  sitting  14  hours,  and  walking  2  hours  spends  about 
2500  Calories ;  whereas  if  he  spends  2  hours  in  vigorous  exer- 
cise instead  of  walking,  his  total  energy  output  rises  to  about 
3000  Calories. 

The  importance  of  muscular  activity  as  the  chief  factor 
governing  the  energy  expenditure  and  food  requirement  of 
healthy  adults  calls  for  a  careful  quantitative  study  of  its  effect 
upon  metabolism. 


CONDITIONS   GOVERNING  ENERGY  METABOLISM        l8l 

Quantitative  relation  between  work  performed  and  total 
metabolism.  —  Theoretically  it  is  possible  to  determine  the 
mechanical  efficiency  of  a  man  by  dividing  the  mechanical 
effect  of  his  work  by  the  increase  of  energy  metabolism  which 
the  work  involves.  This  gives  the  basis  on  which  to  as- 
certain how  much  extra  food  would  be  necessary  to  supply  the 
energy  required  for  the  performance  of  any  given  task. 

Zuntz  and  his  associates  in  Berlin  have  carried  out  a  long 
series  of  experiments  of  this  kind  which  are  described  by  Mag- 
nus-Levy in  Von  Noorden's  Metabolism  and  Practical  Medi- 
cine. The  general  bearing  of  these  experiments  may  be  sum- 
marized as  follows : 

The  amount  of  oxygen  consumed  during  work  in  excess  of 
that  during  rest  was  regarded  as  a  measure  of  that  expended 
upon  the  work.  As  a  rule  the  increased  consumption  of  oxygen 
during  work  is  relatively  greater  than  the  increased  volume  of 
air  breathed,  so  that  a  greater  proportion  of  the  oxygen  of  the 
inspired  air  must  be  taken  up  by  the  lungs.  As  an  example 
of  the  increase  of  oxygen  consumption  with  muscular  work  the 
data  obtained  by  Katzenstein  in  experiments  upon  the  work  of 
walking  up  an  inchned  plane  may  be  given.  The  figures  were 
as  follows : 


Oxygen 
Consumed 
PER  Minute 

Respira- 
tory 
Quotient 

Horizontal 
Distance 

Ascent 

At  rest 

Walking  on  very  slight  incline 

Walking  up  incline  with   10.8 

per  cent  rise 

cc. 

263.75 
763.00 

1253-2 

0.801 
0.805 

0.801 

Meters 
74.48 
67.42 

Meters 

0.58 
7.27 

The  constancy  of  the  respiratory  quotient  indicates  that 
there  was  no  change  in  the  nature  of  the  material  burned  in  the 
body  on  passing  from  rest  to  gentle,  or  from  gentle  to  moderate 


1 82  CHEMISTRY  OF  FOOD  AND   NUTRITION 

exercise  (though  there  is  other  evidence,  as  will  be  seen  below, 
that  vigorous  exercise  is  apt  to  be  accompanied  by  a  rise  in  the 
respiratory  quotient). 

The  weight  moved  (that  of  the  subject  and  his  clothing) 
was  in  this  case  55.5  kilograms.  From  these  data  it  was  cal- 
culated that  a  consumption  of  energy  equivalent  to  0.223  kilo- 
gram-meter was  required  to  move  i  kilogram  of  weight  hori- 
zontally over  a  distance  of  i  meter;  and  2.924  kilogram-meters 
of  energy  to  raise  i  kilogram  through  a  vertical  distance  of  i 
meter. 

Experiments  upon  several  other  subjects  gave  similar  results, 
indicating  that  these  men  who,  while  not  trained  in  an  athletic 
sense,  were  physically  sound  and  thoroughly  accustomed  to 
this  form  of  exercise,  were  able  to  perform  i  kilogram-meter  of 
work  in  the  ascent  of  the  incline  with  an  expenditure  of  only 
about  3  kilogram-meters  of  energy  over  that  required  at  rest, 
so  that  the  work  was  done  with  a  mechanical  efficiency  of  about 
33  per  cent.  It  is  to  be  noted,  however,  that  this  applies  only 
to  walking  done  under  the  most  favorable  conditions,  and  not 
carried  to  the  point  of  fatigue ;  also  that  robust  men  unac- 
customed to  this  form  of  exercise  showed  efficiencies  of  only 
20  to  25  per  cent  until  after  several  days'  practice,  and  for  some 
subjects  the  maximum  efficiencies  found  were  21  to  31  per  cent. 

On  this  basis  it  might  be  estimated  that  a  man  of  average 
weight  in  walking  one  mile  on  level  ground  .would  do  8000-9000 
kilogram-meters  of  work,  or  about  the  mechanical  equivalent 
of  20  Calories.  If  this  were  accomplished  with  an  efficiency  of 
33  per  cent,  it  would  involve  an  expenditure  of  only  60  Calories, 
but  at  an  efficiency  of  20  per  cent  100  Calories  per  mile  would 
be  required. 

The  data  of  Benedict  and  Murschhauser's  recent  experiments 
lead  to  a  similar  conclusion.  They  found  that  the  extra  metab- 
oHsm  involved  in  walking  at  a  speed  of  4  miles  per  hour  aver- 
aged  0.585    gram-calorie   per    kilogram-meter.     For    a    man 


CONDITIONS   GOVERNING  ENERGY  METABOLISM       1 83 

of  70  kilograms  this  would  correspond  to  an  increased  energy 
metabolism  of  about  60  Calories  per  mile.  Very  fast  walking 
(5.4  miles  per  hour)  involved  an  expenditure  of  0.932  gram- 
calorie  per  kilogram-meter,  equivalent  on  the  same  basis  to 
about  95  Calories  per  mile.  To  walk  at  a  speed  of  nearly  5I 
miles  per  hour  required  a  greater  expenditure  of  energy  than  to 
run  at  the  same  speed. 

These  figures  may  be  helpful  in  estimating  the  food  require- 
ments of  men  who  neither  do  active  physical  labor  nor  take 
vigorous  exercise,  yet  move  about  more  freely  than  in  the  so- 
called  rest  experiments  already  described.  If,  for  example, 
it  be  assumed  that  a  healthy  man  would  require  2200  Calories 
per  day  when  remaining  in  one  room,  and  that  the  total  ad- 
ditional muscular  movements  of  a  day  at  business  and  recre- 
ation were  equivalent  to  walking  five  miles  on  level  ground, 
his  total  food  requirement  for  the  day  would  become  2500  to 
2700  Calories  (36  to  39  Calories  per  kilogram),  while  activity 
equivalent  to  walking  ten  miles  on  level  ground  would  bring 
the  total  daily  requirements  to  2800  to  3200  Calories  (40  to  46 
Calories  per  kilogram). 

By  means  of  the  respiration  calorimeter,  Atwater  and  Benedict 
studied  the  question  of  mechanical  efficiency  with  more  accu- 
rate measurements  of  the  energy  involved  than  in  the  experi- 
ments of  the  Zuntz  laboratory,  but  with  a  different  form  of 
muscular  work.  They  placed  in  the  calorimeter  chamber  an 
ergometer,  which  consisted  of  a  fixed  bicycle  frame  having  in 
place  of  the  rear  wheel  a  metal  disk  which  is  revolved  against  a 
measured  amount  of  electrical  resistance,  so  that  the  mechani- 
cal effect  of  the  muscular  work  is  very  accurately  determined. 
The  expenditure  of  energy  involved  in  the  performance  of 
this  work  was  estimated  by  comparing  the  total  metabolism 
of  a  working  day  with  that  of  the  same  man  when  living  in 
the  calorimeter  chamber  at  rest.  The  average  results  obtained 
with  three  different  men  were  as  follows : 


i84 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


Energy  Transformed 

Heat 
Equiv.  of 
Work  Per- 
formed 

Mechan- 
ical 
Efficiency 

Subject  and  Nature  of 
Experiment 

Total 
per  day 

Excess 

over  that 

at  rest 

Subject  E.  0. 
Average  13  rest  experiments 

(42  days) 

Average  3  work  experiments 

(12  days) 

Subject  J.  F.  S. 
Average  4  rest  experiments 

(12  days) 

Average  6  work  experiments 

(18  days) 

Subject  J.  C.  W. 
Average    i    rest   experiment 

(4  days) 

Average  14  work  experiments 

(46  days) 

Calories 

2279 
3892 

2119 
3559 

2357 
5143 

Calories 
1613 

1440 

2786 

Calories 
214 

546 

Per  cent 
13-3 

16.2 

19.6 

With  an  improved  ergometer  of  the  same  type  as  that  used  in  the  ex- 
periments just  cited,  Benedict  and  Carpenter  working  with  J.  C.  W.  (one  of 
the  three  men  above  mentioned)  found  efficiencies  ranging  from  20.7  to  22.1 
per  cent  and  averaging  21.6  per  cent;  with  other  men  studied,  the  efficien- 
cies ranged  from  18.1  to  21.2  per  cent. 

Benedict  and  Cathcart,  in  similar  bicycle  ergometer  experiments  in  which 
the  basis  of  comparison  was  complete  rest  on  a  couch,  found  efficiencies 
varying  from  10  to  25  per  cent,  depending  on  load,  speed,  and  the  familiarity 
of  the  subject  with  the  work,  the  maxima  for  the  six  men  studied  being 
23.1,  20.4,  21.6,  22.7,  20.8,  and  25.2  per  cent  respectively. 

In  another  series  of  experiments  they  subtracted  from  the  expenditure 
of  energy  during  work,  the  amount  spent  when  the  subject,  instead  of  lying 
on  a  couch,  sat  on  the  ergometer  and  allowed  the  pedals  to  be  turned  under 
his  feet.  Using  this  method  of  estimation  they  were  able  by  careful  adjust- 
ment of  speed  and  load  to  realize  with  a  professional  bicycle  rider  an  efficiency 
of  2,2,  per  cent  or  as  much  as  Zuntz  and  his  associates  had  estimated  from  the 
walking  experiments. 


CONDITIONS   GOVERNING  ENERGY  METABOLISM       185 

Only  under  the  most  favorable  circumstances  and  with 
subjects  fully  accustomed  to  the  kind  of  work  being  performed 
will  the  actual  mechanical  effect  produced  amount  to  as  much 
as  one  fourth  to  one  third  of  the  extra  energy  expended  during 
work  over  that  during  rest,  i.e.  to  an  efficiency  of  25  to  33  per 
cent.  Not  only  do  most  occupations  involve  kinds  of  work 
which  in  their  nature  must  be  done  with  less  efficiency  than 
walking  (or  riding  a  stationary  ergometer)  but  the  usual  hours 
of  labor  are  longer  than  those  in  which  the  maximum  mechanical 
efficiency  is  attained.  The  efficiency  may  begin  to  decHne  before 
any  sensation  of  fatigue  is  felt. 

Thus  Leo  Zuntz  found,  when  he  rode  his  bicycle  for  four  successive  hours 
at  an  average  rate  of  15  to  17  kilometers  (about  9  miles)  per  hour,  that  he 
experienced  no  feeling  of  fatigue,  but  his  determinations  showed  that  the 
expenditure  of  energy  necessary  to  produce  a  given  eflFect  had  increased 
about  9,  13,  10,  and  23  per  cent  at  the  end  of  i,  2,  3,  and  4  hours  respectively. 
This  is  because  if  the  same  kind  of  work  be  performed  for  a  series  of  hours, 
auxiliary  muscles  are  gradually  brought  increasingly  into  action,  partly 
for  the  performance  of  the  work  itself,  partly  for  the  fixation  of  the  bodily 
framework  (maintenance  of  posture).  These  auxiliary  muscles  work  less 
economically  than  those  which  are  used  first  and  most  naturally.  For 
much  the  same  reasons  there  is  a  lower  eflSciency  in  the  case  of  work  which 
is  from  the  first  of  too  fatiguing  a  nature  because  of  being  either  excessive 
or  unsuitably  distributed.  When  Leo  Zuntz  increased  his  speed  2.4  times,  he 
found  his  metabohsm  increased  4.3  times,  implying  a  considerable  loss  of 
efficiency.  Under  the  conditions  of  Benedict  and  Cathcart's  experiments 
also,  the  efficiency  was  usually  decreased  upon  increasing  the  speed ;  on  the 
other  hand  a  moderately  heavy  load  was  more  economical  than  a  light  one. 

From  the  data  determined  by  Atwater  and  Benedict,  Lusk, 
Becker,  and  their  respective  collaborators,  it  is  now  possible  to 
estimate  the  approximate  average  expenditure  of  energy  per 
hour  under  a  considerable  number  of  conditions  of  muscular 
activity.  For  convenience  of  comparison  and  application  the 
original  data  have  been  reduced  to  a  common  basis  of  a  man  of 
70  kilograms  (154  pounds),  then  averaged  and  the  average  ap- 


1 86  CHEMISTRY  OF  FOOD  AND   NUTRITION 

proximated  to  the  nearest  "  round  "  number,  with  the  results 
shown  in  the  accompanying  table. 

Energy  Expenditure  of  Average-sized  Man  (70  Kilograms)  per 
Hour  under  Different  Conditions  of  Activity.  (Approximate 
Averages  Only) 

Sleeping 60-70  Calories 

Awake,  lying  stilly 70-85  Calories 

Sitting  at  rest ioo_Calories 

Standing  at  rest 115  Calories 

Tailoring 135  Calories 

Typewriting  rapidly 140  Calories 

Bookbinding 170  Calories 

"Light  exercise"  (bicycle  ergometer) 170  Calories 

Shoemaking 180  Calories 

Walking  slowly  (about  2f  miles  per  hour) 200  Calories 

Carpentry  1 

Metal  working         } 240  Calories 

Industrial  painting  J 

"Active  exercise"  (bicycle  ergometer) 290  Calories 

Walking  actively  (about  3 f  miles  per  hour)       .     .     .     .     .  300  Calories 

Stoneworking 400  Calories 

"Severe  exercise"  (bicycle  ergometer) 450  Calories 

Sawing  wood 480  Calories 

Running  (about  5j  miles  per  hour) 500  Calories 

"  Very  severe  exercise "  (bicycle  ergometer) 600  Calories 

By  the  use  of  these  estimates  the  probable  food  requirement 
for  a  person  of  70  kilograms  (154  pounds)  may  be  calculated 
very  simply,  as,  for  instance,  in  the  following  example: 
8  hours  of  sleep  at  65  Calories  =    520  Calories 

2  hours'  light  exercise  *  at  1 70  Calories  =    340  Calories 
8  hours' carpenter  work  at  240  Calories  =  1920  Calories 
6  hours'  sitting  at  rest  at  100  Calories   =    600  Calories 
Total  food  requirement  for  the  day,        3380  Calories 

Tigerstedt,  in  his  Textbook  of  Physiology,  gives  estimates  of 
food  requirements  for  different  degrees  of  activity  as  indicated 
by  means  of  typical  occupations,  which  may  be  useful  in  check- 
ing results  calculated  as  above. 

*  Going  to  and  from  work,  for  example. 


CONDITIONS   GOVERNING  ENERGY  METABOLISM        187 

According  to  Tigerstedt: 

2000-2400  Calories  per  day  suffice  for  a  shoemaker. 
2400-2700  Calories  per  day  suffice  for  a  weaver. 
2700-3200  Calories  per  day  suffice  for  a  carpenter  or  mason. 
3200-4100  Calories  per  day  suffice  for  a  farm  laborer. 
4100-5000  Calories  per  day  suffice  for  an  excavator. 
Over  5000  Calories  per  day  are  required  by  a  lumberman. 

Lusk  gives  the  following  summary  of  energy  requirements 
of  women  at  work  at  typical  occupations  as  investigated  by 
Becker  and  Hamalainen  in  Finland : 

A  seamstress  sewing  with  a  needle  required  1800  Calories. 

Two  seamstresses,  using  a  sewing  machine,  required  1900 
and  2100  Calories,  respectively. 

Two  bookbinders  required  1900  and  2100  Calories. 

Two  household  servants,  employed  in  such  occupations  as 
cleaning  windows  and  floors,  scouring  knives,  forks,  and 
spoons,  scouring  copper  and  iron  pots,  required  2300  to  2900 
Calories. 

Two  washerwomen,  the  same  servants  as  the  last  named, 
required  2600  and  3400  Calories  in  the  fulfillment  of  their  daily 
work. 

Benedict  and  Cathcart  find  that  when  muscular  work  is 
severe  there  is  a  rise  in  the  respiratory  quotient,  the  rise  being 
greater  the  more  severe  the  work.  In  such  cases  the  respiratory 
quotient  is  found  to  fall  during  the  rest  period  following  the 
work,  and  usually  to  a  lower  figure  than  that  observed  before 
the  work  was  begun.  They  interpret  this  to  mean  that  hard 
muscular  work  draws  upon  the  stored  carbohydrate  of  the  body 
in  slightly  greater  proportion  than  upon  the  stored  fat.  That 
the  work  is  performed  at  the  expense  of  both  carbohydrate 
and  fat  is  shown  by  Benedict  and  Cathcart's  data  as  well  as 
by  those  of  many  previous  experiments.  Apparently  it  is  only 
severe  muscular  activity  which  has  any  appreciable  influence 


l88  CHEMISTRY  OF  FOOD  AND   NUTRITION 

upon  the  relative  proportions  of  fat  and  carbohydrate  burned. 
In  the  experiments  cited  on  page  i8i,  for  example,  the  respira- 
tory quotient  was  not  changed  by  walking  either  on  a  hori- 
zontal surface  or  up  an  inclined  plane.  It  should  also  be  noted 
that  Benedict  and  Cathcart  found  the  same  mechanical  effi- 
ciency in  work  whether  preceded  by  a  carbohydrate-rich  or 
a  carbohydrate-poor  diet. 

Influence  of  Food  upon  Energy  Metabolism 

Atwater  and  Benedict  determined  directly  by  means  of  the 
respiration  calorimeter  the  heat  production  of  the  same  man 
during  five  fasting  experiments  of  one  to  two  days  each,  and 
during  a  four-day  experiment  with  food  about  sufficient  for 
maintenance.  The  average  total  metaboHsm  on  the  fasting 
days  was  about  9  per  cent  lower  than  on  the  days  when  food 
was  taken. 

In  longer  fasts  there  may  be  a  somewhat  greater  decrease  in 
heat  production.  Thus,  Benedict  found  that  a  man  who 
weighed  at  the  start  59.5  kilograms  (131  pounds)  metabolized, 
on  the  successive  days  of  a  seven-day  fast,  1765,  1768,  1797, 
1775,  1649,  1 5 53  J  aiid  1568  Calories  respectively.  Naturally 
in  long  fasts  factors  other  than  the  simple  sparing  of  the  direct 
effect  of  food  come  into  play.* 

Tigerstedt  studied  by  means  of  the  carbon  and  nitrogen  bal- 
ance the  metabolism  of  a  man  who  fasted  for  five  days  and 
for  the  next  two  days  took  a  very  liberal  diet.  The  following 
data  were  obtained: 

*  For  a  detailed  account  of  the  results  obtained  in  a  fasting  experiment  of  3 1 
days'  duration,  see  Benedict,  A  Study  of  Prolonged  Fasting,  Publication  No.  203 
of  the  Carnegie  Institution  of  Washington. 


CONDITIONS  GOVERNING  ENERGY  METABOLISM       189 


Body  Weight 
Kilos 

Calculated 

Total 

Metabolism 

Calories 

Calories 
per 
Kilo 

ist  fast  day 

2d  fast  day 

3d  fast  day 

4tli  fast  day 

5th  fast  day 

Fed  4 14 1  Calories     .     .     . 
Fed  4141  Calories  (2d  day) 

67.0 

65.7 
64.9 
64.0 

63.1 
64,0 
65.6 

2220  * 
2102  * 
2024 
1992 
1970 

2437 
2410 

33.2* 

32.0* 

31.2 

31. 1 

31.2 

38.1 

36.8 

These  results  show  for  man  (as  had  previously  been  shown 
with  dogs)  that  in  fasting  the  total  metaboHsm  continues  at  a 
fairly  constant  rate  in  spite  of  the  fact  that  the  energy  is  ob- 
tained entirely  at  the  expense  of  body  material.  In  this  case, 
the  diet  given  at  the  end  of  the  fasting  period  (4141  Calories) 
was  approximately  double  what  would  have  been  required  for 
maintenance,  but  the  increase  in  energy  metabohsm  was  only 
22.5  per  cent  over  that  of  fasting. 

The  results  of  fasting  experiments  thus  make  it  evident  that 
the  body  has  but  Httle  power  in  the  direction  of  adjusting  its 
energy  metabohsm  to  the  energy  value  of  its  food  supply. 

Rubner  found  that  each  type  of  food  exerted  a  more  or  less 
specific  influence  upon  the  energy  metaboHsm,  so  that  when  the 
foodstuffs  were  fed  separately,  somewhat  different  energy  values 
were  required  for  the  maintenance  of  body  equilibrium.  Thus, 
if  the  total  metabohsm  of  a  dog  fasting  at  33°  C.  be  represented 
by  100  Calories,  he  must  be  fed,  in  order  to  prevent  loss  of 
body  substance,  about  106.5  Calories  of  sugar,  or  114.5  Calories 
of  fat,  or  140  Calories  of  protein.  A  man  observed  by  Rubner 
metabohzed  in  fasting  2042  Calories ;  when  fed  2450  Calories 
in  the  form  of  sugar  alone,  he  metabohzed  2087  Calories ;  when 

*  These  figures  are  slightly  too  high  because  the  loss  of  carbon  on  these  days 
was  due  in  part  to  combustion  of  glycogen,  but  is  calculated  as  if  due  simply  to  pro- 
tein and  fat. 


I90  CHEMISTRY  OF  FOOD  AND   NUTRITION 

fed  2450  Calories  in  the  form  of  meat  alone,  he  metaboHzed  2566 
Calories. 

Recently  Lusk  and  his  coworkers  have  investigated  the  in- 
fluence of  the  foodstuffs  upon  metabolism  C  specific  dynamic 
action  ")  very  extensively  and  have  developed  the  subject  to 
such  an  extent  that  for  an  adequate  discussion  of  their  results 
the  original  articles  ^  or  Lusk's  own  summary  ^  should  be  con- 
sulted. It  appears  from  this  work  that  when  the  digestion 
products  of  carbohydrate  or  fat  are  carried  by  the  blood  to  the 
tissues  the  energy  metabolism  (rate  of  oxidation)  rises  simply 
because  of  the  increased  concentration  of  oxidizable  material; 
but  that  some  of  the  products  of  the  digestion  and  intermediary 
metabolism  of  protein  increase  metaboHsm  not  only  to  a  greater 
extent,  but  also  in  a  somewhat  different  manner,  since  they  seem 
to  act  as  stimuli  rather  than  merely  as  fuel.  On  an  ordinary 
mixed  diet,  however,  this  apparent  loss  of  energy  due  to  eating 
of  protein  is  not  a  very  large  factor  in  the  total  metabolism, 
since  the  total  specific  dynamic  action  makes  the  metabolism 
of  energy  for  the  day  only  about  one  tenth  higher  on  a  full 
maintenance  ration  than  when  no  food  is  eaten. 

Benedict  and  Roth  have  studied  the  energy  metabolism  of 
vegetarians  as  compared  with  non-vegetarians  of  the  same 
height  and  weight  in  order  to  determine  whether  or  not  the 
former  maintain  a  lower  plane  of  basal  metabolism  than  do 
people  who  eat  meat  and  who  are  sometimes  held  to  be  unduly 
stimulated  by  the  protein  of  their  food.  The  energy  metabolism 
was  computed  from  the  carbon  dioxide  production  and  oxygen 
consumption  determined  when  the  subjects  were  at  complete 
rest  and  in  the  "post-absorptive  condition,"  i.e.  at  least  12 
hours  after  the  last  meal,  the  immediate  specific  dynamic  action 
of  the  food  being  thus  practically  excluded.     Under  these  con- 

1  Lusk.  Journal  of  Biological  Chemistry,  Vol.  20,  pages  vii-xvii  and  5SS~6i7. 
Murlin  and  Lusk,  Ibid.,  Vol.  22,  pages  15-20. 

2  Lusk.     Science  of  Nutrition,  Third  Edition,  Chapter  VII. 


CONDITIONS   GOVERNING  ENERGY  METABOLISM        191 

ditions  the  vegetarian  men  and  women  showed  average  basal 
metabolism  of  1.06  and  1.025  Calories  per  kilogram  of  body 
weight  per  hour  respectively,  while  the  corresponding  data  for 
non- vegetarian  men  and  women  were  i.io  and  1.04  Calories 
respectively.  Benedict  holds  that  these  differences  are  too 
small  to  establish  any  essential  difference  in  the  basal  energy 
metabolism  of  vegetarians  and  non-vegetarians  of  like  height 
and  weight. 

It  is  sometimes  thought  that  superior  preparation  or  very 
thorough  mastication  of  food  results  in  such  improvement  in 
its  utilization  that  a  material  saving  may  be  effected  in  the 
amount  of  food  required.  But  it  will  be  remembered  that 
under  average  conditions  only  about  5  per  cent  of  the  energy 
value  of  the  food  is  lost  in  digestion  or  expended  upon  the  di- 
gestive process.  Any  improvement  in  those  conditions  through 
superior  preparation  or  mastication  of  the  food  can  therefore 
at  most  effect  a  saving  of  less  than  five  per  cent  of  the  energy 
value.  Thus  the  influence  upon  total  food  requirement  is 
scarcely  appreciable.  The  advantages  of  good  preparation  and 
thorough  chewing  of  the  food  are  very  important,  but  they  lie 
in  other  directions  than  reduction  in  the  amount  of  food  required. 

Recent  scientific  evidence  supports  the  view  that  chronic 
undernutrition  or  even  simple  restriction  of  food  consumption 
in  health,  if  continued  sufficiently,  may  bring  the  organism  to 
a  lower  level  of  energy  metabohsm  than  would  be  indicated 
by  the  weight  or  surface. 

Regulation  of  Body  Temperature 

Climate,  season,  housing,  clothing,  are  all  factors  which  may 
influence  energy  metabolism  through  their  bearing  upon  the 
regulation  of  body  temperature.*    It  is  evident  that  the  main- 

*  For  full  discussion  of  the  influence  of  surrounding  temperature  upon  metabolism 
and  the  relation  of  metabolism  to  the  regulation  of  body  temperature  the  reader  is 
referred  to  Lusk's  Science  oj  Nutrition. 


192  CHEMISTRY  OF  FOOD  AND  NUTRITION 

tenance  of  the  body  at  a  temperature  above  that  of  its  or- 
dinary environment  involves  a  continual  output  of  heat.  This 
output  of  heat  may  be  regulated  in  either  of  two  ways :  (i)  By 
variations  in  the  quantity  of  blood  brought  to  the  skin,  which 
tend  to  control  the  loss  of  heat  by  radiation,  conduction,  and 
sweating;  this  is  called  *'  physical  regulation."  (2)  By  an  in- 
crease in  the  rate  of  oxidation  in  the  body  in  response  to  the 
stimulus  of  external  cold ;  such  a  change  in  the  rate  of  oxidation 
is  known  as  *'  chemical  regulation."  The  extra  heat  production 
which  follows  the  taking  of  food  (the  specific  dynamic  action 
of  the  foodstuffs)  may  take  the  place  of  the  "  chemical  regu- 
lation "  and  so  help  to  protect  the  body  from  the  necessity  of 
burning  material  simply  for  the  maintenance  of  its  temperature. 
Muscular  work,  by  increasing  the  production  of  heat  in  the  body, 
may  also  render  chemical  regulation  unnecessary;  but  ap- 
parently the  specific  dynamic  action  does  not  furnish  energy 
which  can  be  utilized  for  muscular  work.^ 

The  presence  of  a  layer  of  adipose  tissue  under  the  skin  as 
well  as  the  custom  of  covering  the  greater  part  of  the  external 
surface  with  clothing  also  tends  to  keep  down  the  loss  of  heat  to 
the  point  where  "  physical  regulation  "  will  suffice.  Lusk  cites 
experiments  by  Rubner  upon  a  man  whose  metabolism  was 
determined  when  kept  in  the  same  cold  room  but  with  dif- 
ferent amounts  of  clothing,  and  observes  that  when  the  man 
was  sufficiently  clothed  to  be  comfortable  the  "  chemical  regu- 
lation "  was  eHminated  {Science  of  Nutrition,  3d  edition,  page 
149). 

In  general  it  seems  probable  that  people  warmly  clothed  and 
living  in  houses  which  are  heated  in  winter  are  not  called  upon 
to  exercise  "  chemical  regulation  "  to  any  considerable  extent ; 
in  other  words,  they  probably  do  not  burn  any  considerable 
amount  of  material  merely  for  the  production  of  heat,  the  heat 
required  for  the  maintenance  of  body  temperature  being  ob- 

1  See  Lusk's  Science  of  Nutrition,  3d  edition,  pages  31 1-3 13. 


CONDITIONS  GOVERNING  ENERGY  METABOLISM       193 

tained  in  connection  with  the  metabolism  which  is  essential  to 
the  maintenance  of  the  muscular  tension  and  the  various  other 
forms  of  internal  work.  If,  however,  the  body  be  exposed  to 
cold,  it  may  be  forced  to  employ  "  chemical  regulation  "  with  a 
resulting  increase  of  the  food  requirement,  and  this  will  occur 
more  readily  in  a  thin  person  than  in  one  who  is  well  protected 
by  subcutaneous  fat. 

The  extra  heat  required  in  cold  weather  is  probably  obtained 
for  the  most  part  through  the  activities  of  the  muscles.  It  is 
a  matter  of  general  experience  that  one  instinctively  exercises 
the  muscles  more  vigorously  in  cold  weather  than  in  warm,  and 
if  one  attempts  to  endure  much  cold  without  muscular  exer- 
cise there  results  shivering  —  a  peculiar  involuntary  form  of 
muscular  activity  whose  function  appears  to  be  to  increase 
heat  production  through  increasing  the  internal  work  of  the 
body. 

To  a  large  extent,  therefore,  the  regulation  of  body  tempera- 
ture, in  case  of  exposure  to  cold,  is  accomplished  through  the 
activity  and  tension  of  the  muscles. 

The  foregoing  discussion  has  reference  primarily  to  adults. 
In  the  case  of  the  infant  whose  surface  is  much  greater  in  pro- 
portion to  his  weight  and  whose  muscular  tone  is  not  yet  fully 
developed,  the  loss  of  heat  to  the  surroundings  is  not  so  readily 
checked  by  "  physical  "  nor  so  easily  made  good  by  "  chemical  " 
regulation.  Unless  the  infant  is  either  warmly  clothed  or  sup- 
pHed  with  an  artificial  source  of  heat  in  cold  weather  he  may  be 
forced  to  burn,  for  warmth,  material  that  might  better  be  em- 
ployed for  growth. 

The  Influence  of  Age  and  Growth 

From  the  fact  that  in  animals  of  the  same  species,  but  of 
different  size  the  heat  production  is  proportional  to  the  surface 
rather  than  to  the  weight,  it  would  follow  that  children  must 
have  a  greater  food  requirement  per  unit  of  weight  than  adults. 


194 


CHEMISTRY  OF   FOOD  AND   NUTRITION 


In  a  child  2  years  old  weighing  25  pounds  the  energy  metabolism 
is. approximately  half  as  great  as  in  an  adult  of  six  times  this 
weight,  i.e.  the  energy  expenditure  per  unit  of  weight  is  three 
times  as  great  for  the  young  child  as  for  the  resting  man,  and 
while  for  the  man  the  expenditure  may  be  taken  as  a  measure  of 
the  requirement,  in  the  case  of  the  child  an  additional  allowance 
must  be  made  to  provide  the  material  retained  in  the  body  for 
growth.  In  studies  of  infants  7  to  9  months  old,  Rubner  and 
Heubner  found  a  storage  of  12.2  per  cent  of  the  energy  value 
of  the  food  consumed,  and  Camerer  found  a  storage  of  15  per 
cent  of  the  energy  and  40  per  cent  of  the  protein  of  the  diet. 

The  following  data  from  Tigers tedt  illustrate  the  relative 
intensity  of  metaboHsm  at  different  ages : 


Weight 
Kgm. 

Metabolism  per  Day 

Subject 

Total 
Calories 

Per  Kgm. 
Calories 

Per 

Square  Meter 

Calories 

Child,  2  weeks      .     .     . 
Child,  10  weeks     .     .     . 
Child,  10  years     ,     .     . 
Man  at  rest      .... 

3-2 

23.2 
70.0 

258 

420 

1462 

2240 

81.0 
84.0 
63.0 
32.0 

■     1000 
1200 
1499 
1071 

According  to  these  observations  the  metabolism  per  unit  of 
weight  is  greatest  in  infancy  and  decHnes  steadily  with  increas- 
ing size ;  but  calculated  per  unit  of  surface  it  is  distinctly  less 
in  infancy  than  in  children  of  10  years,  probably  because  the 
infant  sleeps  a  greater  proportion  of  the  time  and  the  tension 
(tonus)  of  its  muscles  is  not  yet  fully  developed. 

As  between  children  and  adults  the  energy  metabolism  is 
more  nearly  proportional  to  the  surface  than  to  the  weight; 
but  among  children  of  about  the  same  age  the  energy  require- 
ment may  be  computed  on  the  basis  of  weight  about  as  well  as 
on  the  basis  of  surface. 


CONDITIONS  GOVERNING  ENERGY  METABOLISM       195 

Murlin  and  Bailey  estimate  from  their  own  observations, 
and  the  earlier  ones  of  Benedict  and  Talbot,  that  the  energy 
requirement  of  the  newborn  baby  kept  comfortably  warm  and 
sleeping  quietly  may  be  placed  tentatively  between  1.7  and  2.0 
Calories  per  kilogram  per  hour,  the  lower  figure  for  a  very  fat 
(10  lb.)  child  and  the  higher  for  a  thin  (6  lb.)  child.  Accord- 
ing to  these  authors  even  vigorous  crying  does  not  raise  this 
figure  more  than  40  per  cent.  Benedict  and  Talbot  in  th^  ^ 
later  pubHcation  ^  give  measurements  of  minimum  heat  pro- 
duction of  94  newborn  infants  (2  hours  to  6  days  old)  which 
range  from  1.33  to  2.17  Calories,  averaging  1,75  Calories  per 
kilogram  per  hour.  "  Maximum  "  energy  metabolism,  chiefly 
due  to  vigorous  crying,  was  also  observed  in  93  of  these  cases 
and  found  to  average  65  per  cent  above  the  resting  value,  while- 
in  several  instances  (10  out  of  93)  '*  crying  and  extreme  rest- 
lessness "  resulted  in  energy  expenditure  more  than  double 
that  of  the  same  infant  at  rest. 

With  the  development  of  the  musculature  and  of  muscular 
tonus,  the  energy  expenditure  of  the  normal  infant  increases 
for  a  time  even  more  rapidly  than  his  body  weight,  so  that  at 
from  2  months  to  i  year  of  age  the  expenditure  of  energy  while 
sleeping  averages  2.7  Calories  per  kilogram  per  hour  (average 
of  Rowland's,  Benedict  and  Talbot's,  and  MurUn  and  Hoobler's 
data  as  summarized  by  the  latter).  During  the  waking  hours 
the  rate  of  expenditure  is  of  course  materially  higher,  and  in 
calculating  food  requirements  allowance  must  be  made  for 
growth  and  for  the  possibility  of  losses  through  imperfect 
utilization  of  the  food.  In  order  to  provide  adequately  for  all 
contingencies  and  support  the  rapid  growth  which  is  normal 
at  this  age,  it  is  estimated  that  a  vigorous  child  will  require 
during  the  greater  part  of  the  first  year  about  100  Calories  of 
food  per  kilogram  of  his  body  weight  per  day.     But  in  cases 

1  Physiology  of  the  New  Born  Infant,  Publication  No.  233,  Carndfeie  Institution 
of  Washington,  191 5. 


196  CHEMISTRY  OF  FOOD  AND  NUTRITION 

of  artificial  feeding,  since  the  digestive  tract  must  be  gradually 
educated  to  handle  the  milk  of  a  different  species,  it  will  often 
be  necessary  to  feed  much  less  than  100  Calories  per  kilogram 
per  day  at  first,  perhaps  for  several  months,  and  only  very 
gradually  increase  the  food  allowance. 

From  the  end  of  the  first  year  until  growth  is  completed  the 
food  requirement  increases,  but  not  so  rapidly  as  does  the  body 
weight,  so  that  while  the  allowance  of  food  becomes  larger  per 
day  it  becomes  smaller  per  kilogram.  On  the  latter  basis  the 
energy  requirement  at  the  different  ages  may  be  estimated 
approximately  as  follows : 

Under    i  year  100  Calories  per  kilogram       (45  Calories  per  lb.) 

1-2  years  100-90  Calories  per  kilogram  (45-40  Calories  per  lb.) 

2-  5  years  90-80  Calories  per  kilogram  (40-36  Calories  per  lb.) 

6-  9  years  80-70  Calories  per  kilogram  (36-32  Calories  per  lb.) 

10-13  years  75-60  Calories  per  kilogram  (34-27  Calories  per  lb.) 

14-17  years  65-50  Calories  per  kilogram  (30-22  Calories  per  lb.) 

18-25  years  55-40  Calories  per  kilogram  (25-18  Calories  per  lb.) 

Children  who  are  very  active  or  growing  very  rapidly  may 
require  even  more  food  than  the  table  just  given  suggests. 
Such  cases  are  perhaps  most  frequently  found  among  boys 
between  10  and  15  years  of  age.  DuBois  finds  in  boys  12  and 
13  years  old  an  average  hasal  metabolism  (complete  rest  and 
almost  complete  fasting)  of  1.76  Calories  per  kilogram  per  hour, 
or  about  75  per  cent  above  that  of  healthy  adults.*  Assuming 
average  activity  for  boys  of  this  age  the  energy  expenditure 
during  24  hours  would  probably  amount  to  60  to  70  Calories 
per  kilogram  and  as  this  is  a  period  of  rapid  growth  the  require- 
ment would  be  materially  higher  than  the  rate  of  expenditure. 

Assuming  average  size  at  the  different  ages  the  allowances  in 
Calories  per  day  become  about  as  follows  if 

*  Per  unit  of  surface  the  basal  energy  metaboKsm  of  these  boys  was  about  25 
per  cent  higher  than  that  of  healthy  men. 

t  See  also  the  more  detailed  table  of  energy  allowances  for  children  in  Chapter 
XIV. 


CONDITIONS  GOVERNING  ENERGY  METABOLISM       197 


Children  of  1-2  years  inclusive 
Children  of  2-  5  years  inclusive 
Children  of  6-  9  years  inclusive 
Girls  of  10-13  years  inclusive 
Boys  of  10-13  years  inclusive 
Girls  of  14-17  years  inclusive 
Boys        of  14-17  years  inclusive 


1000-1200 
I 200-1 500 
1400-2000 
1800-2400 
2300-3000 
2200-2600 
2800-4000 


Calories 
Calories 
Calories 
Calories 
Calories 
Calories 
Calories 


per  day 
per  day 
per  day 
per  day 
per  day 
per  day 
per  day 


In  estimating  the  food  requirement  of  a  family  it  is  usually 
preferable  to  consider  each  child's  energy  requirement  directly 
rather  than  to  count  the  children  as  equivalent  to  fractions  of 
the  hypothetical  "  average  man." 

Above  the  age  of  17  years,  although  there  is  still  some 
growth,  differences  in  activity  due  to  occupation  become  so 
great  that  the  food  requirement  will  usually  depend  as  much 
upon  occupation  as  upon  age. 

The  fuel  value  of  children's  dietaries  should  always  be 
liberal  in  order  to  provide  amply  for  muscular  activity  and  for 
a  more  intense  general  metabolism  than  that  of  the  adult. 
Furthermore,  throughout  the  period  of  growth  the  food  must 
supply  a  certain  amount  of  material  to  be  added  to  the  body 
in  the  form  of  new  tissue  in  addition  to  all  that  which  is  oxidized 
to  support  metabolism. 


Age 

Height 

Weight 

Food  Requirement 

WITHOUT  Muscular 

Labor 

Years 

Meters 

Feet  and 
inches 

Kilos 

Lbs. 

Total  per 
day  Calories 

Per.  Kgm. 
per  day 
Calories 

I 

5 
10 

15 
20 

30 
40 
60 

70 

80 

0.70 
1. 00 
1.28 

1. 71 
1.72 
1.71 

2:3 
3:3 
4:2 

5:7  + 
5:8- 
5:7  + 

10 

17 
26 

50 
65 
69 
70 
68 
65 
63 

22 

37 

57 

no 

143 
152 
154 
150 
143 
139 

1000 
1400 
1800 
2800 
3000 
2750 
2500 
2300 
2000 
1750 

100 
82 
70 
56 
46 
40 
36 
34 
31 
28 

198 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


With  the  elderly,  on  the  other  hand,  the  intensity  of  metab- 
olism is  diminished  and  the  body  not  only  needs  less  food, 
but  has  less  ability  to  deal  with  excess,  so  that  the  food  re- 
quirement gradually  decHnes  and  may  become  10  or  20  per 
cent,  or  possibly  even  30  per  cent,  lower  than  in  middle  life. 

In  the  table  on  page  197  are  given  the  estimated  height, 
weight,  and  food  requirement  of  an  average  man  at  different  ages, 
the  figures  for  height  and  weight  being  based  upon  the  data 
given  by  Hill  for  males  of  the  Anglo-Saxon  and  Teutonic  races 
(Recent  Advances  in  Physiology  and  Biochemistry,  page  284). 

These  estimates  of  food  requirements  are  intended  to  repre- 
sent approximate  averages  of  available  data  and  to  allow  for 
such  exercise  as  would  naturally  be  taken  at  the  age,  exclusive 
of  anything  which  would  ordinarily  be  considered  physical 
labor.  They  thus  illustrate  in  an  approximate  way  the  rate 
at  which  the  amount  of  food  required  for  healthy  maintenance 
per  unit  of  body  weight  declines  from  infancy  to  old  age. 

DuBois  has  recently  published  in  graphic  form  his  estimates 
of  the  basal  energy  metabolism  per  unit  of  body  surface  at 
different  ages.  The  graph  is  reproduced  by  Lusk  {Science  0] 
Nutrition,  3d  edition,  page  128). 

The  average  basal  metabolism,  per  unit  of  surface,  found  by 
DuBois  in  boys  of  12  to  13,  in  men,  and  in  women  was  as  follows: 

Average  Basal  Metabolism  of  Boys,  Men,  and  Women  (DuBois) 


Age  in  Years 

Calories  per  Hour  per  Square 
Meter 

Subjects 

Computed  accord- 
ing to  Meeh's 
formula 

Computed  by 
DuKois  height- 
weight  formula 

Boys 

Men 

Women 

Men       

W^omen 

Men 

12-13 
20-50 
20-50 
50-60 
50-60 
77-83  ■ 

45.7 
34-7 
32.3 
30.8 
28.7 

49.9 
39-7 

36.9 
35.2 
32.7 

35-1 

CONDITIONS   GOVERNING  ENERGY  METABOLISM       199 

Influence  of  sex.  —  Whether  sex  shall  be  said  to  influence 
the  energy  requirement  will  depend  upon  our  use  of  terms. 
Boys  spend  on  the  average  more  energy  than  girls,  and  men 
more  than  women,  but  it  is  doubtful  if  the  differences  are  due 
to  other  causes  than  have  been  considered  above.  In  experi- 
ments in  which  children  were  allowed  to  move  about  in  a 
small  respiration  room,  boys  were  found  to  expend  decidedly 
more  energy  than  girls  of  the  same  age  and  weight ;  but 
this  was  probably  due  to  the  greater  restlessness  and  muscular 
tension  of  the  boys,  for  in  another  series  in  which  both  boys 
and  girls  were  kept  motionless  and  relaxed  during  the  obser- 
vations the  difference  was  not  found.  Benedict  and  Emmes 
found,  as  noted  above,  a  slightly  higher  basal  metabolism  in 
men  than  in  women  of  the  same  height  and  weight,  but 
attribute  this  to  a  difference  in  the  average  composition  of 
the  body. 

While  sex  alone  seems  not  to  be  a  measurable  factor  in 
energy  metabolism,  the  performance  of  the  reproductive  func- 
tions may  make  large  demands  upon  the  maternal  organism. 
As  weight  increases  during  pregnancv  energy  metabolism 
increases  in  at  least  equal  proportion.  In  the  last  two  "weeks 
of  human  pregnancy  Murlin  finds  the  energy  metaboHsm  per 
unit  of  weight  about  4  per  cent  higher  than  for  non-pregnant 
women.  During  lactation,  when  the  entire  nutritive  require- 
ment of  the  nursing  infant  is  being  met  through  the  mother, 
the  energy  needs  of  the  latter  are  greatly  increased.  Pro- 
duction of  milk  involves  an  extra  energy  requirement  much 
beyond  the  actual  energy  value  of  the  milk  secreted.  While 
accurate  determinations  are  not  at  hand,  it  seems  safe  to 
conclude  that  the  nursing  mother  taking  only  moderate 
exercise  may  need  as  much  food  as  a  man  at  muscular  work. 
Liberal  feeding  of  the  nursing  mother  {e.g.  up  to  2800  to 
3000  Calories  for  a  woman  with  moderate  muscular  exercise) 
is  not  only  important  for  the  conservation  of  her  own  bodily 


200  CHEMISTRY  OF  FOOD  AND  NUTRITION 

resources  but  may   prolong  the  period  of  lactation  and  thus 
be  of  great  value  to  the  child  as  well.^ 

REFERENCES 

Anderson  and  Lusk.  The  Interrelation  between  Diet  and  Body  Condi- 
tion and  the  Energy  Production  during  Mechanical  Work.  Journal  oj 
Biological  Chemistry,  Vol.  32,  page  421  (191 7). 

Armsby.     Principles  of  Animal  Nutrition,  Chapters  6  and  11. 

Armsby  and  Fries.  Influence  of  Standing  or  Lying  upon  the  Metabolism 
of  Cattle.    American  Journal  of  Physiology,  Vol.  31,  page  245  (1912). 

Atwater.  Neue  Versuche  ueber  Stoff-  und  Kraft-wechsel.  Ergebnisse 
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Atwater,  Benedict,  et  al.  Respiration  Calorimeter  Experiments.  Bul- 
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AuB  AND  DuBois.  The  Basal  Metabolism  of  Old  Men.  Archives  of 
Internal  Medicine,  Vol.  19,  page  823  (191 7). 

Bailey  and  Murlin.  The  Energy  Requirement  of  the  Newborn.  Amer- 
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Becker  et  al.  Energy  Metabolism  during  Different  Kinds  of  Work. 
Skandinavisches  Archiv  der  Physiologic,  Vol.  31,  (a  series  of  papers) 
—  (1914). 

Benedict.  Metabolism  during  Fasting.  Carnegie  Institution  of  Wash- 
ington, Publication  Nos.  77  and  203. 

Benedict.  Factors  Affecting  Basal  Metabolism.  Journal  of  Biological 
Chemistry,  Vol.  20,  page  263  (191 5). 

Benedict  and  Carpenter.  The  Metabolism  and  Energy  Transformations 
of  Healthy  Man  during  Rest.  Carnegie  Institution  of  Washington, 
PubUcation  No.  126. 

Benedict  and  Carpenter.  The  Influence  of  Muscular  and  Mental  Work 
on  Metabolism  and  the  Efficiency  of  the  Human  Body  as  a  Machine. 
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of  Agriculture. 

Benedict  and  Cathcart.  Muscular  Work :  A  Metabolism  Study  with 
Special  Reference  to  the  Efficiency  of  the  Human  Body  as  a  Machine. 
Carnegie  Institution  of  Washington,  Publication  No.  187. 

Benedict  and  Emmes.    The  Influence  upon  Metabolism  of  Non-oxidizable 

1  For  general  discussion  of  the  problem  of  maintaining  breast  feeding,  see  papers 
by  Sedgwick,  Abt,  and  Hoobler  in  the  Journal  of  the  American  Medical  Association 
for  Aug.  II,  1917  (Vol.  69,  pages  417-428). 


CONDITIONS   GOVERNING  ENERGY  METABOLISM      20I 

Material  in  the  Intestinal  Tract.    American  Journal  of  Physiology ^ 

Vol.  30,  page  197  (1912). 
Benedict  and  Emmes.    A  Comparison  of  the  Basal  Metabolism  of  Normal 

Men  and  Women.    Journal  of  Biological  Chemistry,  Vol.   20,  pages 

253-262  (1915). 
Benedict  and  Roth.    The  Metabolism  of  Vegetarians  as  compared  with 

Non- Vegetarians  of  Like  Height  and  Weight.    Journal  of  Biological 

Chemistry,  Vol.  20,  pages  231-241  (1915). 
Benedict  and  Smith.    The  Metabolism  of  Athletes.    Journal  of  Biological 

Chemistry,  Vol.  20,  pages  243-251  (1915). 
Benedict  and  Talbot.     Respiratory  Exchange  of    Infants.     American 

Journal  of  Diseases  of  Children,  Vol.  8,  pages  1-49  (1914). 
Carpenter.    Increase  in  Metabolism  during  the  Work  of  Typewriting. 

Journal  of  Biological  Chemistry,  Vol.  9,  pages  231-266  (1911). 
Carpenter  and  Murlin.     Energy  Metabolism  of  Mother  and  Child  just 

before  and  just  after  Birth.     Archives  of  Internal  Medicine,  Vol,  7, 

pages  184-222  (1911). 
DuBois.     Respiration   Calorimetry  in  Clinical  Medicine.     Harvey  Lec- 
tures, 1915-1916. 
DuBois.    The  Basal  Energy  Requirement  of  Man.    Journal  of  Washington 

Academy  of  Sciences,  Vol.  6,  page  347  (1916). 
DuBois.    The  Metabolism  of  Boys  12  and  13  Years  Old  as  Compared  with 

Metabolism  at  Other  Ages.     Archives  of  Internal  Medicine,  Vol.  17, 

page  887  (1916). 
DuBois  and  Associates.     (A  Series  of  Articles  on  Metabohsm  in  Disease.) 

Archives  of  Internal  Medicine,  Vols.  15  and  17  (1915,   1916).     (The 

reader  may  also  find  other  papers  of  this  series  in  volumes  published 

subsequently  to  the  compiling  of  this  list.) 
DuBois  and  DuBois.    Measurement  of  the  Surface  Area  of  Man.    Ar- 
chives of  Internal  Medicine,  Vol.  15,  pages  868-881  (1915). 
DuBois  and  DuBois.    A  Formula  to  Estimate  the  Approximate  Surface 

Area  if  Height  and  Weight  Be  Known.     Archives  of  Internal  Medicine, 

Vol.  17,  pages  863-871  (1916), 
Gephart  AND  DuBois.     Basal  Metabohsm.     Archives  of  Internal  Medicine, 

Vol.  15,  page  835;  Vol.  17,  page  902  (1915,  1916). 
Krogh.    The  Respiratory  Exchange  of  Animals  and  Man. 
LowY  AND  ZuNTz.     Influence  of  War  Diet  upon  the  Metabolism.    Berlin 

klinische  Wochenschrift,  Vol.  53,  page  825  (1916). 
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LusK.     The   Influence   of   Food   on   Metabolism.    Journal   of  Biological 

Chemistry,  Vol.  20,  pages  vii-xvii  and  555-617  (1915). 


202  CHEMISTRY  OF  FOOD   AND   NUTRITION 

Mathews.    Physiological  Chemistry,  Chapter  XIII. 

Means.     Basal    Metabolism   and   Body   Surface.    Journal   of  Biological 

Chemistry,  Vol.  21,  pages  263-268  (191 5). 
Means,  Aub,  and  DuBois.    The  Efifect  of  Caffeine  on  the  Heat  Production. 

Archives  of  Internal  Medicine,  Vol.  19,  page  832  (191 7). 
MoRGULis.    The  Influence  of  Underfeeding  and  of  Subsequent  Abundant 

Feeding  on  the  Basal  Metabolism  of  the  Dog.     Biochemical  Bulletin, 

Vol.  3,  page  264  (1914). 
MuRLiN.    A  Respiration  Incubator  for  the  Study  of  the  Energy  Metabolism 

of  Infants.     American  Journal  of  Diseases  of  Children,  Vol.  9,  pages 

43-58  (January,  1915). 
MuRLiN  AND  HooBLER.     The  Energy  Metabolism  of  Ten  Hospital  Chil- 
dren between  the  Ages  of  Two  Months  and  One  Year.     American 

Journal  of  Diseases  of  Children,  Vol.  9,  pages  81-119  (February,  1915). 
MuRLiN  AND  LusK.     The  Influence  of  the  Ingestion  of  Fat.     Journal  of 

Biological  Chemistry,  Vol.  22,  page  15  (1915). 
SjosTROM.     The  Influence  of  the  Temperature  of  the  Surrounding  Air  on 

the    Carbon   Dioxide   Output   in   Man.     Skandinavisches   Archiv   der 

Physiologic,  Vol.  30,  pages  1-72  (1913). 
SoDERSTROM,  Meyer,  AND  DuBois.     A  Comparison  of  the  Metabolism  of 

Men  Flat  in  Bed  and  Sitting  in  a  Steamer  Chair.    Archives  of  Internal 

Medicine,  Vol.  17,  page  872  (191 6). 
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Special  Reference  to  Total  Energy  Requirement.     American  Journal 

of  Diseases  of  Children,  Vol.  i\,  page  25  (191 7). 
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and  when  Stimulated.     American  Journal  of  Physiology,  Vol.  32,  pages 

107-145   (1913).     See  also:    Proceedings  of  the  National  Academy  of 

Sciences,  Vol.  i,  page  no  (1915). 
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Biochemische  Zeitschrift,  Vol.  55,  pages  341-354  (1914). 


CHAPTER  VIII 

FACTORS   DETERMINING   THE   PROTEIN 
REQUIREMENT 

Animal  cells  under  all  conditions  of  life  are  constantly  break- 
ing down  proteins  into  simpler  substances  which  the  body  elimi- 
nates. Since  this  breaking  down  or* "  cataboHsm  "  of  protein 
does  not  stop  either  in  fasting  or  under  the  most  Hberal  feeding 
with  fats  and  carbohydrates,  it  follows  that  there  is  always  a 
need  for  protein  whatever  the  supply  of  other  food. 

Protein  metabolism  differs  widely  from  energy  metabolism  in 
the  conditions  which  determine  its  amount,  for  protein  metab- 
oKsm  is  governed  mainly  by  the  kind  and  amount  of  food,  and 
to  only  a  sHght  extent  if  at  all  by  muscular  exercise ;  whereas 
energy  metabohsm  is  governed  mainly  by  the  muscular  exer- 
cise, and  to  only  a  relatively  small  extent  by  the  food.  By 
giving  food  rich  in  fats  and  carbohydrates  but  poor  in  protein, 
the  protein  metabolism  of  a  healthy  man  can  easily  be  brought 
to  less  than  50  grams  per  day,  and  then  by  changing  to  a  diet 
rich  in  protein,  it  may  be  increased  to  150  or  even  200  grams 
per  day;  i.e.  the  rate  of  protein  metabohsm  can  be  increased 
200  to  300  per  cent  in  a  few  days  by  a  change  in  diet  alone,  all 
other  conditions  remaining  the  same. 

Protein  Metabolism  in  Fasting 

Since  the  diet  has  such  a  great  influence  upon  the  amount  of 
protein  metaboHzed,  it  might  be  expected  that  the  basal  protein 
metabohsm  could  be  observed  best  in  fasting.  But  in  fasting 
the  energy  metabolism  of  the  body  is  only  a  little  lower  than 

203 


204 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


with  food;  the  amount  of  combustion  continues  nearly  the 
same  although  only  body  material  is  available;  and  since  the 
body  must  consume  so  much  of  its  own  substance  to  obtain  the 
energy  needed,  there  is  always  a  chance  that  in  fasting  some  pro- 
tein may  be  burned  simply  as  fuel.  Accordingly  the  protein 
metaboHsm  in  fasting  may  be  greater  than  that  which  repre- 
sents the  needs  of  the  body  when  properly  fed,  while  on  the 
other  hand  it  may  be  abnormally  low  through  the  effort  of  the 
body  to  adjust  itself  to  the  abnormal  condition. 

The  amount  of  protein  broken  down  in  fasting  is  much  in- 
fluenced (i)  by  the  previous  habit  as  regards  protein  consump- 
tion, and  (2)  by  the  metabolism  of  stored  glycogen  and  stored  fat. 

The  direct  effect  of  the  level  of  protein  metabolism  on  the  days 
preceding  the  fast  is  shown  in  the  following  data  obtained  by 
Voit  in  experiments  upon  a  dog  weighing  35  kilograms : 

Influence  of  Previous  Diet  on  Nitrogen  Elimination  in  Fasting 

(Voit) 


Foods  of  Preceding  Days  and  Grams  of  Urea 

PER  Day 

Meat  2500  grams 

Meat  1500  grams 

Bread 

Last  day  with  food  .     .     . 

180.8 

IIO.8 

24.7 

First  day  of  fasting  . 

60.1 

29.7 

19.6 

Second  day  of  fasting 

. 

24.9 

18.2 

15.6 

Third  day  of  fasting 

19.1 

17.5 

14.9 

Fourth  day  of  fasting 

17.3 

14.9 

13-2 

Fifth  day  of  fasting  . 

. 

12.3 

14.2 

12.7 

Sixth  day  of  fasting      .     . 

13.3 

I3-0 

130 

The  influence  of  the  metabolism  of  the  previously  stored  glycogen 
upon  the  amount  of  protein  metaboHzed  in  fasting  is  well  illus- 
trated by  the  following  three  experiments  with  one  individual :  ^ 

1  Benedict,  Inflmnce  of  Inanition  on  Metabolism.  Carnegie  Institution  of  Wash- 
ington (1907). 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     20$ 


First  Day  of  Fasting 

Second  Da\ 

OF  Fasting 

Experiment 

Glycogen  metabo- 
lized 

Nitrogen  elimi- 
nated 

Glycogen  metabo- 
Uzed 

Nitrogen  elimi- 
nated 

grams 

grams 

grams 

grams 

.    I 

181.6 

5.84 

29.7 

11.04 

II 

135-3 

10.29 

18.I 

11.97 

III 

64.9 

12.24 

23.1 

12.45 

It  will  be  seen  that  the  nitrogen  output  was  less  when 
there  was  available  for  metabolism  a  considerable  supply  of 
previously  stored  glycogen.  Since  most  of  the  stored  glycogen 
is  used  up  on  the  first  day  of  fasting,  its  influence  upon*  the 
protein  metabolism  is  short-lived  as  compared  with  that  of  the 
stored  fat. 

The  influence  of  the  available  supply  of  body  fat  upon  the 
protein  metabolism  of  fasting  is  shown  by  the  following  obser- 
vations of  Falck,  on  the  protein  metaboHsm  of  two  fasting  dogs 
—  the  one  lean,  the  other  fat : 


Faxck's  Lean  Dog 


Fasting  days 


1-4 

5-8 

9-12 

13-16 

17-20 

21-24 


Grams  protein  catab- 
olized  per  day 


26.1 
24.6 

33.9 
38.0 

31-9 
3-9 


On  the  25th  day  the  dog  died. 


Falck 's  Fat  Dog 


Fasting  days 


1-6 
7-12 
13-18 
19-24 
25-29 
30-34 
35-38 
40-44 

45-50 
55-60 


Grams  protein  catab- 
olized  per  day 


29.9 
26.7 
26.1 
22.3 
20.0 
16.8 
15-7 
130 
13.6 
12.2 


Dog  still  healthy  after  60  days. 


2o6  CHEMISTRY  OF  FOOD  AND  NUTRITION 

A  rise  in  protein  metabolism  of  the  lean  dog  after  the  8th  day 
showed  that  from  this  time  he  used  protein  largely  as  fuel  —  so 
largely  that  the  results  were  fatal  in  25  days  of  fasting.  The 
fat  dog,  having  plenty  of  other  fuel  in  the  form  of  fat,  used 
protein  to  a  much  smaller  extent,  so  that  he  was  able  gradually 
to  accommodate  himself  to  a  lower  level  of  protein  metaboHsm 
and  to  endure  a  fast  of  60  days'  duration. 

The  professional  faster,  Succi,  starting  with  a  good  store  of 
body  fat,  fasted  30  days  *  with  the  following  results : 

Five  days  on  ordinary  food    .     .     .  101.4  grams  protein  per  day 

X-  5th  days  fasting 80.4  grams  protein  per  day 

6-1  oth  days  fasting 53.1  grams  protein  per  day 

I  i-i  5th  days  fasting 36.2  grams  protein  per  day 

i6-2oth  days  fasting 33.1  grams  protein  per  day 

21-2 5th  days  fasting 29.3  grams  protein  per  day 

26-3oth  days  fasting 33.3  grams  protein  per  day 

Since  Succi's  health  remained  good  throughout  his  fast,  it 
might  be  thought  that  the  true  protein  requirement  of  his  body 
was  not  greater  than  the  smallest  figure  found  for  any  period 
—  in  this  case  about  30  grams  per  day.  On  the  other  hand,  it 
may  well  be  supposed  that,  since  the  body  increases  its  protein 
metabolism  to  an  abnormally  high  rate  under  influence  of  exces- 
sive protein  feeding,  so  under  the  influence  of  fasting  the  body 
may  be  able  to  adjust  itself  to  an  abnormally  low  rate  of  pro- 
tein metabolism ;  and  the  fact  that  the  protein  metabolism  con- 
tinues to  diminish  for  such  a  long  time  in  fasting  gives  weight  to 
the  supposition  that  the  body  is  here  gradually  adapting  itself  to 
an  abnormal  condition.  One  might  assume  that  in  some  par- 
ticular period  of  Succi's  fast,  the  effect  of  previous  feeding  might 
no  longer  be  apparent  and  the  conditions  had  not  yet  become 
abnormal  as  the  result  of  the  fasting,  in  which  case  the  ex- 
penditure of  protein  during  one  of  these  periods  would  represent 
his  normal  requirement.     Any  such  assumption  must,  however, 

*  The  output  of  nitrogen  and  of  several  other  elements  during  a  31 -day  fast 
recently  described  by  Benedict  may  be  found  in  Chapter  IX. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     207 

be  more  or  less  arbitrary.  A  much  more  definite  idea  of  the 
normal  dietary  need  is  obtained  by  determining  experimentally 
how  much  protein  must  be  contained  in  the  daily  food  in  order 
to  keep  the  body  in  protein  (or  nitrogen)  equilibrium. 

Nitrogen  Balance  Experiments  and  the  Tendency  toward 
Equilibrium  at  Different  Levels  of  Protein  Intake 

The  estimation  of  the  nitrogen  balance  has  already  been  re- 
ferred to  as  one  factor  in  the  determination  of  the  total  food  re- 
quirement by  means  of  metabolism  experiments ;  and  it  has 
been  shown  that  the  balance  may  be  found  either  by  comparing 
the  total  intake  with  the  total  output,  or  by  comparing  the 
amount  absorbed  with  the  amount  catabolized  and  eliminated 
through  the  kidneys.*  When  intake  exceeds  output,  there  is  a 
plus  balance  which  indicates  a  storage  of  nitrogen  and  therefore 
of  protein  in  the  body;  a  minus  balance  (greater  output  than 
intake)  indicates  a  loss  of  body  protein.     When  the  balance  is 

0,  or  so  near  o  as  to  be  within  the  Kmits  of  experimental  error, 
the  body  is  said  to  be  in  nitrogen  (or  protein)  equilibrium. 

The  healthy  full-grown  body  tends  to  estabHsh  nitrogen 
equilibrium  by  adjusting  its  rate  of  protein  metabohsm  to  its 
food  supply  within  wide  limits.  The  time  required  by  the  body 
for  this  adjustment  depends  mainly  upon  the  extent  to  which 
the  diet  is  changed. 

The  following  observations  by  Von  Noorden  illustrate  the  estab- 
hshment  of  equiHbrium  after  only  moderate  changes  in  the  diet : 

A  young  woman  weighing  58  kilograms  (128  pounds)  at  rest  in 
bed  was  given  food  furnishing  protein,  106  grams ;  fat,  7 1 .6  grams ; 
carbohydrate,  200  grams ;  fuel  value,  i860  Calories  per  day. 

*  Theoretically  the  elimination  through  the  skin  should  also  be  determined  and 
included  in  the  calculation ;  practically  this  is  usually  neglected  unless  on  account 
of  warm  weather  or  vigorous  exercise  the  subject  has  perspired  profusely.  For 
data  on  nitrogen  in  perspiration  see  Benedict,  Journal  of  Biological  Chemistry,  Vol. 

1,  page  263  (1906)  and  A  Study. of  Prolonged  Fasting,  Publication  No.  203  of  the  Car- 
negie Institution  of  Washington,  pages  233-235. 


2o8 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


Example  of  Adjustment  to  Diminished  Intake 

Total  nitrogen  of  food 16.96  grams 

Lost  in  digestion  (nitrogen  in  feces)        .94  gram 

"Absorbed" 16.02  grams 


Nitrogen  Catabolized 

AND  Eliminated 

Nitrogen  Balance 

THROUGH  Kidneys 

grams 

grams 

I  St  day 

18.2 

-  2.18 

2d  day    .     . 

17.0 

-  0.98 

3d  day    .     . 

15.8 

+  0.22 

4th  day 

•  V    •    •    •    • 

16.0 

+  0.02 

5th  day 

15-7 

+  0.32 

Here  there  was  practical  equilibrium  after  the  second  day. 
The  small  amount  of  nitrogen  represented  as  stored  on  the 
third,  fourth,  and  fifth  days  was  very  likely  lost  through  the 
skin.  This  was  a  case  of  adjustment  to  a  lowered  protein  in- 
take, for  the  food  previously  taken,  although  not  accurately 
observed,  was  known  to  have  been  rich  in  protein. 

Another  experiment  was  made  by  Von  Noorden  with  the 
same  patient  to  show  the  time  required  to  reach  equilibrium 
after  increasing  the  intake  of  protein.  In  tkis  case  the  food 
furnished  2030  Calories  per  day  and  the  nitrogen  balance  was  as 
follows : 

Example  of  Adjustment  to  Increased  Intake 


Day 

Nitrogen 
IN  Food 

Nitrogen  in 
Feces 

Nitrogen 
"  Absorbed  " 

NriROGEN 

Catabollzed 

Nitrogen 
Balance 

grams 

gram 

grams 

grams 

grams 

I 

14.40 

0.70 

13.70 

13.60 

+  O.IO 

2 

14.40 

0.70 

13-70 

13.80 

—  O.IO 

3 

14.40 

0.70 

13.70 

13.60  • 

+  0,10 

4 

20.96 

0.82 

20.14 

16.80 

+  3.34 

5 

20.96 

0.82 

20.14 

18.20 

+ 1.94 

6 

20.96 

0.82 

20,14 

19.50 

+  0,64 

7 

20.96 

0.82 

20.14 

20,00 

+  0,14 

FACTORS  DETERMINING  PROTEIN  REQUIREMENT     209 

Here  where  the  amount  of  protein  fed  was  increased  from  90 
to  130  grams  without  change  in  the  total  fuel  value  of  the  diet, 
the  body  reached  equihbrium  on  the  fourth  day  after  the 
increase. 

It  is  apparent  therefore : 

(i)  That  the  body  tends  to  adjust  its  protein  metabolism  to 
its  protein  supply. 

(2)  That  when  the  body  is  accustomed  to  a  certain  rate  of 
protein  metaboHsm,  it  requires  an  appreciable  length  of  time  to 
adjust  itself  to  a  materially  higher  or  lower  rate.  ^ 

Hence  the  rate  of  protein  metabolism  on  any  given  day  will 
depend  in  part  upon  the  rate  of  metabolism  to  which  the  body 
has  been  accustomed  and  in  part  upon  the  protein  intake  for 
the  day.  When  the  protein  supply  varies  from  day  to  day,  the 
metaboHsm  for  each  day  is  influenced  by  both  the  factors,  with 
the  net  result  that  the  ehmination  equals  the  intake  when 
averaged  for  a  sufficiently  long  period,  although  the  data  for 
any  particular  day  might  show  a  distinct  gain  or  loss.  When 
the  protein  supply  is  constant  for  a  few  days,  the  effect  of  pre- 
vious habit  usually  disappears  and  equihbrium  is  estabhshed  as 
in  the  above  cases. 

A  transitory  loss  of  nitrogen  from  the  body  is  apt  to  be  due 
simply  to  the  taking  of  less  than  the  usual  amount  of  protein 
food,  but  a  persistent  loss  indicates  that  the  diet  is  insufficient, 
either  in  total  food  (calories)  or  in  protein,  to  enable  the  usual 
adjustment  to  take  place. 

A  transitory  storage  of  nitrogen  in  the  body  may  occur  as  the 
result  of  an  increase  either  of  the  protein  or  of  the  total  fuel 
value  of  the  food ;  but  a  persistent  storage  occurs,  as  Von  Noor- 
den  has  pointed  out,  only  under  the  following  conditions : 

(i)  In  the  growing  body  (or  in  pregnancy)  where  new  tissue 
is  being  constructed. 

(2)  In  cases  where  increased  muscular  exercise  calls  for  en- 
largement of  the  muscles. 


2IO  CHEMISTRY  OF  FOOD  AND  NUTRITION 

(3)  In  cases  where,  owing  to  previous  insufficient  feeding  or 
to  wasting  disease,  the  protein  content  of  the  body  has  been 
more  or  less  diminished  and  consequently  any  surplus  available 
is  utiHzed  to  make  good  the  loss. 

Protein-sparing  Action  of  Carbohydrates  and  Fats 

It  has  been  shown  above  that,  in  fasting  experiments,  the 
amount  of  stored  glycogen  and  fat  in  the  body  exerts  a  "  spar- 
ing "  influence  upon  protein  metabolism,  the  amount  of  protein 
catabohzed  being  smaller  when  the  supplies  of  glycogen  and  fat 
are  more  abundant.  Similarly  the  amounts  of  carbohydrates 
and  fats  in  the  food  influence  the  rate  of  protein  metaboHsm  as 
indicated  by  the  nitrogen  excretion.  The  loss  of  protein  which 
occurs  on  an  insufficient  diet  may  be  diminished  or  even  stopped 
by  adding  carbohydrates  or  fat  to  the  food;  and  if  carbo- 
hydrate or  fat  be  added  to  the  diet  of  a  man  in  nitrogen  equi- 
librium, there  results  a  temporary  decrease  in  nitrogen  output 
with  a  corresponding  storage  of  protein  in  the  body.  The  former 
observation  could  be  interpreted  as  meaning  simply  that  the 
body  draws  upon  its  stored  protein  for  energy  so  long,  and  only 
so  long,  as  the  fuel  value  of  the  food  is  insufficient ;  but  the  fact 
that  addition  of  carbohydrate  or  fat  to  a  diet  already  sufficient 
may  cause  an  actual  storage  of  protein  indicates  that  the  "  pro- 
tein-sparing action  "  or  "  protein-protecting  power  "  of  carbohy- 
drates and  fats  involves  something  more  than  merely  the  question 
whether  the  body  "  needs  "  to  burn  its  stored  protein  as  fuel. 

As  this  is  a  matter  of  great  importance,  it  may  be  well  to 
consider  somewhat  carefully  (i)  the  experimental  evidence,  and 
(2)  the  theoretical  explanations,  regarding  the  protein-sparing 
action  of  the  carbohydrates  and  fats.  For  an  account  of  the 
earlier  experiments  on  this  subject,  especially  those  of  Voit  and 
Rubner  upon  dogs,  the  reader  is  referred  to  Lusk's  Elements  of 
the  Science  of  Nutrition.  Only  some  of  the  more  important  of 
the  experiments  upon  men  can  be  described  here. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     211 

Lusk/  experimenting  upon  himself,  showed  the  susceptibility 
of  the  protein  metaboHsm  to  the  sudden  withdrawal  of  carbo- 
hydrate food.  In  one  experiment  a  liberal  mixed  diet  contain- 
ing 20.55  grams  of  nitrogen  was  taken  until  the  body  was  nearly 
in  nitrogen  equilibrium,  and  then,  without  any  other  change, 
350  grams  of  carbohydrate  were  withdrawn  from  the  daily 
food.  On  the  first  day  the  body  protein  was  largely  protected 
by  the  carbohydrate  previously  stored  in  the  body  in  the  form 
of  glycogen,  but  on  the  second  day  the  nitrogen  metabolism 
had  risen  from  19.84  to  27.00  grams  per  day.  In  another  experi- 
ment, upon  a  diet  containing  less  protein,  withdrawal  of  carbo- 
hydrate increased  the  nitrogen  excretion  from  11.44  to  17.18 
grams  per  day. 

In  these  cases,  as  in  the  fasting  experiments,  the  loss  of  body 
protein  was  less  in  those  subjects  having  a  good  store  of  body 
fat  than  in  those  which  were  thin. 

Kayser  compared  the  efficiency  of  carbohydrates  and  fats  as 
sparers  of  protein  by  observing  the  effect  upon  the  nitrogen 
balance  of  replacing  the  carbohydrates  of  the  food  by  such  an 
amount  of  fat  as  would  furnish  the  same  number  of  calories, 
and  then  after  three  days  resuming  the  original  diet.  This 
experiment  and  that  of  Tallquist  which  follows  are  given  some- 
what fully,  as  they  illustrate  well  the  methods  and  results  of 
investigations  based  mainly  upon  the  question  of  nitrogen  equi- 
librium. The  observer,  who  served  as  his  own  subject,  was 
twenty-three  years  old,  of  good  physique,  with  a  small  store  of 
body  fat,  and  weighed  67  kilograms.  In  the  first  and  third 
periods  he  ate  meat,  rice,  butter,  cakes,  sugar,  oil,  vinegar,  and 
salad.  In  the  second  period  the  diet  was  changed  so  as  to  con- 
sist of  meat,  eggs,  oil,  vinegar,  and  salad,  so  that  practically  all 
the  carbohydrate  was  withdrawn  and  replaced  by  fat.  The  two 
diets  had  practically  the  same  fuel  value  and  protein  content. 
The  results  of  this  experiment  are  shown  in  the  following  table : 

1  Zeitschrijt  Jiir  Biologie,  Vol.  27,  page  459  (1890). 


212 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


Nitrogen  Balance  when  Feeding  Isodynamic  Quantities  of  Carbo- 
hydrate AND  Fat  (Kayser) 


Intake 

Output 

Nitrogen 
Balance 

Day 

Total 
nitrogen 

Fat 

Carbo- 
hydrates 

Fuel 
value 

Total 
nitrogen 

grams 

grams 

grams 

Calories 

grams 

grams 

I 

21.15 

71. 1 

338.2 

2590 

18.66 

+  2.46 

2 

21.15 

71.8 

338.2 

2596 

20.04 

+  1.11 

3 

21.15 

71.8 

338.2 

2596 

20.59 

+  0.56 

4 

21.31 

71.8 

338.2 

2600 

21.31 

=t  0.00 

5 

21.51 

221. 1 

000.0 

2607 

23.28 

-  1.77 

6 

21.55 

217.0 

000.0 

2570 

24.03 

-  2.48 

7 

21.55 

215.5 

000.0 

2556 

26.53 

-4.98 

8 

21.10 

70.4 

338.2 

2581 

21.65 

-0.55 

9 

21.10 

70.4 

338.2 

2581 

19.20 

+  1.89 

lO 

21.10 

70.4 

338.2 

2581 

19.65 

+  1.45 

It  is  evident  from  the  nitrogen  balance  of  the  first  period  that 
the  amount  of  protein  in  the  food  was  here  greater  than  neces- 
sary, but  that  equiHbrium  was  fully  established  in  four  days. 
r  On  substituting  fat  for  carbohydrate  there  is  a  marked  increase 
of  protein  cataboHsm  with  corresponding  loss  of  nitrogen  from 
the  body,  and  what  is  especially  noteworthy,  there  was  no  evi- 
dence of  any  tendency  to  regain  equilibrium  during  this  period, 
but  on  the  contrary  the  loss  of  nitrogen  became  greater  each 
day  the  fat  diet  was  continued ;  whereas,  upon  returning  to  the 
mixed  diet,  not  only  was  the  loss  of  protein  stopped,  but  the 
body  almost  at  once  began  replacing  the  protein  it  had  lost, 
although  the  nitrogen  and  calories  of  the  food  were  practically 
unchanged, 

Tallquist^  compared  the  protein-protecting  powers  of  iso- 
dynamic amounts  (amounts  having  equal  energy  value)  of  car- 

1  Archivjiir  Hygiene,  Vol.  41,  page  177. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     213 

bohydrates  and  fats  when  only  a  part  of  either  was  replaced  by 
the  other.  The  subject  was  Tallquist  himself,  a  man  twenty- 
eight  years  old,  in  good  health,  and  weighing  about  80  kilograms. 
The  experiment  was  performed  in  Rubner's  laboratory,  and  the 
diet  contained  such  an  amount  of  total  food  as  was  estimated  by 
Rubner  to  be  just  about  sufficient  to  supply  the  energy  require- 
ments of  the  body,  viz.,  36  Calories  per  kilogram  per  day.  The 
experiment  covered  8  days  divided  into  two  equal  periods.  In 
the  first  four-day  period  the  diet  was  rich  in  carbohydrates,  in 
the  second  period  it  was  rich  in  fats.  An  excellent  feature  of 
this  experiment  is  that  there  was  no  change  in  the  nature  of  the 
protein  fed.  All  foods  furnishing  any  significant  amount  of 
nitrogen  were  the  same  in  the  two  periods  of  the  experiment. 

The  food  of  the  first  period  consisted  of  meat,  milk,  butter, 
bread,  sugar,  coffee,  beer.  That  of  the  second  period  contained 
the  same  amounts  of  meat,  milk,  bread,  coffee,  and  beer,  but 
less  sugar,  more  butter,  and  some  bacon.  The  same  amount  of 
salt  was  taken  in  each  case.  The  principal  data  of  the  experi- 
ment may  be  summarized  as  follows : 

Nitrogen  Balance  when  Feeding  Isodynamic  Quantities  of  Carbo- 
hydrate AND  Fat  (Tallquist) 


Intake 

OuTPxrr 

Nitrogen 
Balance 

Day 

Total 
nitrogen 

Fat 

Carbo- 
hydrates 

Alcohol 

Fuel 
value 

Nitrogen 

grams 

grams 

grams 

grams 

Calories 

grams 

I 

16.27 

44.0 

466 

18.5 

2867 

17.11 

-  0.84 

2 

16.27 

44.0 

466 

18.5 

2867 

14.40 

+  1.86 

3 

16.27 

44.0 

466 

18.5 

2867 

14.65 

+  1.62 

4 

16.27 

44.0 

466 

18.5 

2867 

15.58 

-f  0.69 

5 

16.08 

140.0 

250 

19.0 

2873 

17.66 

-1.58 

6 

16.08 

140.0 

250 

19.0 

2873 

17.32 

-  1.24 

7 

16.08 

140.0 

250 

19.0 

2873 

15.94 

+  0.14 

8 

16.08 

140.0 

250 

19.0 

2873 

16,22 

—  0.14 

214 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


Here  only  a  part  of  the  carbohydrate,  about  half  of  that 
present,  and  an  amount  representing  about  one  third  of  the  total 
fuel  value  of  the  diet,  was  replaced  by  fat.  The  change  evi- 
dently had  an  unfavorable  influence  upon  the  nitrogen  balance 
but  the  loss  of  body  protein  was  relatively  small  and  continued 
only  2  days. 

Atwater  ^  compared  the  protein-sparing  action  of  carbo- 
hydrate and  fat  in  experiments  in  which  the  subject,  an  athletic 
young  man  of  76  kilos,  performed  a  considerable  amount  of 
work.  The  experiments  were  carried  out  in  the  respiration 
calorimeter  and  covered  in  all  15  experimental  days  upon  a  diet 
rich  in  carbohydrates,  arranged  in  four  periods  which  were  alter- 
nated with  four  equal  periods  in  which  the  diet  was  rich  in  fats. 
The  change  from  carbohydrate  to  fat  and  vice  versa  involved 
about  2000  Calories  or  nearly  half  the  fuel  value  of  the  diet. 
The  average  results  per  day  for  the  entire  series  of  experiments 
were  as  follows : 


On  Diet  Rich  in 
Carbohydrates 

On  Diet  Rich  in  Fat 

Available  Calories  in  food      .     . 

4532 

4524        ,^-— ■ 

Heat   equivalent   of   work   per- 

formed, Calories 

558 

554 

Nitrogen  in  food,  grams     .     .     . 

17-5 

17.1 

Nitrogen  in  feces,  grams    .     .     . 

2.5 

1.7 

Nitrogen  in  urine,  grams  .     .     . 

16.6 

18.1 

Nitrogen  balance,  grams    .     .     . 

-  1.6 

-  2.7 

Here  again  there  is  a  difference  in  favor  of  the  carbohydrate, 
but  one  which  is  so  small  as  to  be  of  almost  no  practical  sig- 
nificance. 

It  appears  that  the  carbohydrate  of  the  food  cannot  be  en- 
tirely replaced  by  an  equal  number  of  calories  in  the  form  of  fat 
without  an  unfavorable  effect  upon  the  nitrogen  balance ;   but 

1  Ergebnisse  der  Physiologic,  Vol.  3,  Part  I,  page  497. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     21 5 

that  when  the  replacement  is  such  as  to  affect  not  over  one  half 
of  the  total  calories,  the  difference  in  protein-sparing  action  is 
but  slight.  Ordinarily  on  a  normal  mixed  diet  the  same  num- 
ber of  calories  has  about  the  same  protein-sparing  effect. 

Landergren  ^  also  found  that  it  is  only  when  the  carbohydrate 
of  the  diet  is  entirely  replaced  by  fat  that  the  comparison  is  so 
strikingly  against  the  fat  as  it  seemed  to  be  in  Kayser's  experi- 
ment. In  Landergren's  experiments  the  condition  studied  was 
not  one  of  approximate  equilibrium,  but  rather  of  nitrogen 
hunger.  He  fed  men  diets  of  adequate  fuel  value  but  contain- 
ing only  about  one  gram  of  nitrogen  daily,  and  found  that  by 
four  days  of  such  feeding  the  urinary  nitrogen  may  be  reduced 
to  about  4  grams  per  day.  In  one  experiment  in  which  the  daily 
food  contained  750  grams  of  carbohydrates  the  urine  of  the 
fourth  day  showed  3.76  grams  of  nitrogen.  The  carbohydrate 
was  then  entirely  replaced  by  fat,  with  the  result  that  the  fol- 
lowing days'  urines  contained  respectively  4.28,  8.86,  and  9.64 
grams  of  nitrogen.  Evidently  in  the  case  of  a  man  accustomed 
to  feeding  largely  upon  carbohydrates  the  complete  replacement 
of  carbohydrate  by  fat  leads  to  a  loss  (or  an  increased  loss)  of 
body  protein.  But  by  subsequent  experiments  of  the  same 
series  it  was  found  that  a  diet  containing  nearly  half  its  calories 
in  carbohydrate,  and  nearly  half  in  fat,  had  apparently  the  same 
protein-sparing  power  as  one  made  up  almost  exclusively  of 
carbohydrates.  ^ 

The  explanation  offered  by  Landergren  is  that  when  the  diet 
suppHes  no  carbohydrate,  the  glycogen  of  the  body  soon  be- 
comes exhausted,  and  the  carbohydrate  needed  to  keep  up  the 
constant  glucose  content  of  the  blood  is  obtained  largely  by  the 
breaking  down  of  proteins. 

This  might  suffice  to  explain  the  difference  in  effect  of  carbo- 
hydrate and  fat,  but  not  the  fact  that  addition  of  a  non-nitroge- 

1  Skandinavisches  Archiv  fiir  Physiologic,  Vol.  14,  page  112  (1903) ;  Abstract  Ex- 
periment Station  Record,  Vol.  14,  page  1099. 


2l6 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


nous  nutrient  to  a  diet  already  suflSicient  may  cause  storage  of 
nitrogen  in  the  body.* 

A  satisfactory  explanation  of  both  sets  of  facts  appears  to  be 
afforded  by  the  recent  advances  in  our  knowledge  of  the  fate 
of  foodstuffs  in  metabolism  which  were  outlined  in  Chapter  V. 
The  outstanding  relationships  of  the  three  groups  of  foodstuffs 
in  the  intermediary  metabohsm  may  be  indicated  schematically 
as  follows : 


CARBOHYDRATE 
Glucose 


FAT 

e.g.,  Stearin 

>^  \ 

Stearic  acid     Glycerol 

^  Glyceric 
aldehyde       ^ ' 

By  y9-oxidation, 
finally,  to  carbon 
dioxide  and  water 


PROTEIN 


Amino  acids, 
(Among  which) 


^Methyl  glyoxal 


Alanine 
-+NH3 


Lactic  acid- 

Pyruvic  acid 

By  oxidation,  finally, 
to  carbon  dioxide 
and  water 


Since  ammonia  is  always  being  formed  in  protein  catabohsm 
(by  deaminization  of  amino  acids) ,  and  since  the  ammonium  salts 
of  a-ketonic  acids,  such  as  pyruvic  acid,  are  convertible  into  amino 
acids  which  are  building  materials  for  body  protein,  we  have 
here  a  mechanism  by  which  an  intermediary  product  of  carbo- 
hydrate metabolism  (pyruvic  acid)  takes  up  a  "  waste  product  " 
of  protein  metabolism  (ammonia)  and  turns  it  back  into  amino 
acid  again.  Thus  carbohydrate,  in  undergoing  metabolisms^ 
"  spares  "  protein,  not  only  by  serving  as  fuel  so  that  protein 

*  Furthermore  Lusk  points  out  that  Landergren's  explanation  is  hardly  ade- 
quate to  cover  the  results  obtained  in  gelatin-feeding  experiments. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     217 

need  not  be  drawn  upon  for  this  purpose,  but  also  by  furnishing 
material  which  in  combination  with  ammonia  (otherwise  a 
waste  product)  can  actually  be  converted  in  the  body  into  some 
of  the  amino  acids  of  which  body  proteins  are  composed  and 

.with  which  they  are  in  equihbrium.  This  explains  how  an  in- 
creased intake  of  carbohydrate,  with  resulting  increase  of  pyruvic 
acid,  naturally  leads  to  increased  synthesis  of  amino  acids  and 
thus  to  a  tendency  toward  protein  storag6>  or,  to  express  the 
same  thing  in  somewhat  different  terms,  tends  to  push  the  re- 
action, Amino  acids  ^  Protein,  toward  the  right. 

According  to  present  theory,  most,  if  not  all,  of  the  energy  of 
the  carbohydrate  becomes  available  through  oxidation  processes 
which  involve  the  intermediate  production  of  pyruvic  acid,  an 
a-ketonic  acid  whose  ammonium  salt  is  capable  of  conversion 
into  amino  acid.  Of  the  fat  only  the  glyceryl  radicle  (about 
one  twentieth  of  the  fuel  value)  is  oxidized  through  pyruvic 
acid,  while  the  fatty  acid  radicles,  representing  about  nineteen 
twentieths  of  the  energy  of  the  fat,  are  metaboHzed  through 
)8-oxidation  processes  which  yield,  so  far  as  we  know,  no  product 
whose  ammonium  salt  is  convertible  into  amino  acid  in  the  body. 

'^ence  complete  withdrawal  of  carbohydrate,  even  though  sub-"^ 
stituted  by  sufficient  fat  to  yield  an  equal  number  of  calories, 
must  be  expected  to  result  in  increased  excretion  of  nitrogen; 
but  when  no  more  than  half  of  the  carbohydrate  is  replaced  by 
fat  there  seems  to  be  enough  pyruvic  acid  produced  to  meet  the 
practical  requirements  of  economical  metaboUsm  of  protein. 

Protein  Requirement  in  Normal  Nutrition 

From  what  has  been  said  above  it  will  be  apparent  that, 
within  rather  wide  hmits,  the  greater  the  amounts  of  carbo- 
hydrates and  fats  eaten,  the  smaller  will  be  the  amount  of  pro- 
tein required  to  maintain  nitrogen  equihbrium. 

For  practical  purposes,  however,  we  may  eliminate  the  ques- 
tion of  the  extent  to  which  protein  metaboHsm  can  be  restricted 


2l8  CHEMISTRY  OF  FOOD  AND  NUTRITION 

by  the  use  of  excessive  amounts  of  other  food  and  reduce  the 
problem  to  this :  When  the  total  food  is  properly  adjusted  to  the 
size  and  activity  of  the  subject  so  that  there  is  sufficient  but 
not  excessive  fuel  to  meet  all  the  energy  requirements,  how 
much  protein  must  the  daily  food  contain  in  order  to  keep  the 
body  in  nitrogen  equihbrium? 

The  most  extended  investigation  on  the  protein  requirement 
of  man  is  that  of  Chittenden.*  The  general  plan  followed  in 
this  investigation  was  to  have  each  man  reduce  his  protein  food 
gradually  without  any  great  change  in  his  other  habits.  This 
gradual  reduction  of  the  protein  intake  was  continued  usually 
for  some  weeks,  sometimes  for  several  months,  before  any  com- 
parison of  intake  and  output  was  attempted.  During  this  pre- 
Hminary  period  upon  a  restricted  diet  there  was  in  almost 
every  case  a  loss  of  weight,  and  from  previous  observations  f 
under  similar  conditions  we  may  safely  assume  that  there  was  a 
considerable  loss  of  body  protein.  After  a  sufficient  period  of 
adjustment  there  was  usually  a  tendency  for  the  body  weight 
and  the  rate  of  protein  metaboHsm  (measured  by  the  amount 
of  nitrogen  eliminated  through  the  kidneys)  to  become  fairly 
constant,  indicating  that  the  body  had  adapted  itself  to  the  new 
conditions.  When  this  point  had  been  reached,  a  nitrogen 
balance  experiment  was  made,  the  intake  and  output  being 
determined  by  weighing  and  analyzing  for  nitrogen  all  food 
consumed  and  all  nitrogenous  material  given  off  from  the  body 
except  that  in  the  perspiration.  The  fuel  value  of  the  food 
consumed  during  the  same  period  was  calculated  by  means  of 
figures  taken  from  standard  tables.  From  these  calculated  fuel 
values  it  would  appear  that  the  energy  of  food  consumed  by 
Chittenden's  subjects  was  in  general  about  equal  to  the  usual 
estimates  of  the  energy  requirements  for  similar  occupations, 

*  See  Chittenden's  Physiological  Economy  in  Nutrition  and  Nutrition  of  Man. 

t  Neumann,  for  example,  in  35  days  on  insufficient  diet  lost  96  grams  of  nitrogen 
corresponding  to  600  grams  of  protein,  equivalent  to  about  2.5  kilograms  (5.5  pounds) 
of  muscle  tissue. 


FACTORS   DETERMINING  PROTEIN  REQUIREMENT      219 

though  in  several  specific  instances  the  subject  may  have  unduly 
restricted  his  total  food  intake  and  thus  created  an  energy 
deficit  and  a  tendency  toward  negative  nitrogen  balance. 

Chittenden  bases  his  estimate  of  the  protein  requirement,  not 
only  upon  the  nitrogen  balances,  but  also  upon  the  amounts 
of  nitrogen  observed  to  be  eUminated  daily  through  the  kidneys 
over  long  periods  in  which  the  body  may  or  may  not  have  been 
in  complete  equilibrium,  but  in  which  health  and  efficiency  were 
certainly  maintained.  The  first  men  to  serve  as  subjects  in  this 
investigation  were  Chittenden  himself  and  his  associates,  who 
all  continued  their  professional  work  and  either  reported  no 
effect  or  felt  benefited  by  the  change  to  the  low  protein  diet. 
Similar  experiments  were  then  made  upon  a  squad  of  soldiers, 
who  during  the  test  were  quartered  near  the  laboratory  and  were 
given  regular  exercise  in  the  gymnasium  in  addition  to  Hght 
duties  about  their  quarters.  These  men  showed  marked  im- 
provement in  physical  condition  during  the  test,  probably  due 
in  part  to  their  more  regular  habits  of  Hfe  and  their  gymnastic 
exercises.  In  order  to-  eHminate  this  latter  factor  while  still 
applying  the  low  protein  diet  to  young  and  physically  active 
men,  the  investigation  was  extended  to  cover  a  group  of  uni- 
versity athletes  who  were  already  well- trained  and  in  prime 
physical  condition  at  the  beginning  of  their  dietary  experiment. 
These  athletes  not  only  maintained,  but  in  many  cases  improved, 
their  gymnastic  records  while  on  the  low  protein  diet,  one  of 
them  winning  an  all-round  gymnastic  championship  during 
the  time.  Chittenden  states^  that  his  data  '' are  seemingly 
harmonious  in  indicating  that  the  physiological  needs  of  the 
body  are  fully  met  by  a  metabohsm  of  protein  matter  equal  to 
an  exchange  of  o.io  to  0.12  gram  of  nitrogen  per  kilogram  of 
body  weight  per  day,  provided  a  sufficient  amount  of  non- 
nitrogenous  foods,  is  taken  to  meet  the  energy  requirements  of 
the  body."     This  would  correspond  to  44  to  53  grams  of  pro- 

^  Nutrition  of  Man,  pages  226,  272. 


220  CHEMISTRY  OF  FOOD  AND   NUTRITION 

tein  per  day  for  a  man  of  average  weight  (70  kilograms,  154 
pounds,  without  clothing),  and  Chittenden  considers  that  for 
such  a  man  an  allowance  of  60  grams  of  protein  per  day  should 
certainly  be  entirely  adequate. 

In  a  recent  examination  of  the  available  literature  upon  this 
subject  there  were  found  86  experiments  upon  adults  showing 
no  abnormality  of  digestion  or  health,  in  which  the  diet  was 
sufficiently  well  adjusted  to  the  probable  requirement  and  the 
nitrogen  balance  showed  sufficient  approach  to  equilibrium  to 
make  it  appear  that  the  total  output  of  nitrogen  might  be  taken 
as  an  indication  of  the  protein  requirement.  These  experi- 
ments are  taken  from  20  independent  investigations  in  which  41 
different  individuals  (37  men  and  4  women)  served  as  subjects. 
For  purposes  of  comparison  the  daily  output  of  total  nitrogen  in 
each  experiment  was  calculated  to  protein  and  this  to  a  basis  of 
70  kilograms  of  body  weight.  Reckoned  in  this  way,  the  ap- 
parent protein  requirement  as  indicated  by  the  data  of  individual 
experiments  ranged  between  the  extremes  of  20.0  and  79.2  grams, 
averaging  49.2  grams  of  protein  per  man  of  70  kilograms  per  day. 
Thus  the  average  falls  well  within  the  range  of  Chittenden's 
estimate  of  the  amount  of  protein  required  for  normal  nutrition 
when  the  energy  value  of  the  diet  is  adequate. 

Examination  of  the  data  recorded  in  the  original  papers  indi- 
cates that  the  wide  differences  in  amounts  of  protein  catabolized 
in  the  different  experiments  cannot  be  attributed  primarily  to 
the  kind  of  protein  consumed  nor  to  the  use  of  diets  of  fuel 
values  widely  different  from  the  energy  requirements.  Ap- 
parently the  most  influential  factor  was  the  extent  to  which  the 
subject  had  become  accustomed  to  a  low  protein  diet. 

Difference    between    Minimum    Requirement    and    Standard 
Allowance  of  Protein 

It  may  be  well  to  point  out  here  the  distinction  between  the 
amount  of  protein  actually  required  on  the  one  hand,  and,  on 


-FACTORS  DETERMINING  PROTEIN  REQIHREMENT     221 

the  other  hand,  the  amount  which  it  may  be  thought  best  to 
allow  in  the  planning  of  dietaries.  The  term  "  requirement " 
should  preferably  be  applied  only  to  the  former;  the  latter 
would  better  be  called  the  protein  allowance  or  the  standard 
for  protein.  The  difference  between  the  amount  actually  re- 
quired and  the  amount  which  would  ordinarily  be  allowed  in 
planning  a  dietary  is  much  greater  with  protein  than  with  fuel 
value.  Surplus  fuel  is  stored  as  fat,  and  if  excessive  fatness  is 
to  be  avoided,  the  fuel  value  of  the  food  must  not  greatly  exceed  ♦ 
the  energy  requirements  of  the  body;  but  surplus  nitrogen  is 
rapidly  ehminated  from  the  body  and,  so  long  as  no  injury  to 
health  results,  leaves  no  evidence  of  having  been  taken  in  excess 
of  body  needs.  The  eating  of  a  considerable  surplus  of  protein 
has  become  habitual,  and  such  a  surplus  of  protein  in  the  food  / 
is  beheved  by  many  people  to  constitute  a  desirable  "  factor  of  [ 
safety,"  if  not  indeed  to  exert  a  directly  beneficial  effect  upon 
health  and  stamina.  Hence  there  is  a  tendency  to  set  the  pro- 
tein allowance  or  standard  for  protein  considerably  higher  than 
the  actual  requirement. 

If  the  average  daily  food  requirement  of  a  man  at  rest  be 
taken  as  2000  Calories  including  50  grams  of  protein,  the  same 
man  at  work  may  require  3000  or  4000  Calories  while  his  actual 
requirement  for  protein  will  not  be  appreciably  increased.  If 
the  protein  be  held  at  50  grams  while  the  food  is  increased  from 
2000  to  3000  to  4000  Calories,  the  protein  in  percentage  of  total 
calories  would  be  in  the  three  cases  10  per  cent,  7  per  cent,  and 
5  per  cent  respectively.  Thus  it  is  plain  that  when  the  energy 
requirement  is  subjected  to  considerable  variations  by  differ- 
ences in  muscular  activity,  the  protein  requirement  cannot  be 
taken  as  constituting  a  fixed  proportion  of  the  total  calories, 
since  muscular  work  increases  the  energy  requirement  very 
greatly  and  the  protein  requirement  very  little  if  at  all.  In 
practice,  however,  a  diet  of  2000  Calories  would  usually  contain 
somewhat  over  50  grams  of  protein ;  and  when  the  man  increased 


222  CHEMISTRY  OF  FOOD  AND  NUTRITION 

his  activity  and  his  total  food  consumption,  he  would  probably 
increase  his  protein  intake  in  almost  the  same  proportion,  for 
he  would  in  most  cases  simply  eat  a  larger  quantity  of  his  usual 
kind  of  food. 

Moreover,  those  differences  in  food  requirement  which  are 
due  to  differences  in  age  and  size  will  usually  affect  the  energy 
requirement  and  the  protein  requirement  in  about  the  same 
proportion ;  and,  as  the  majority  of  dietaries  are  planned  for 
family  groups,  th€  differences  in  age  and  size  are  usually  quite 
as  important  as  the  differences  in  muscular  activity.  Thus 
there  is  rational  basis  for  the  custom  of  allowing  enough  pro- 
tein to  furnish  from  lo  to  15  per  cent  of  the  total  energy  value 
of  the  diet. 

Influence  of  the  Choice  of  Food 

When  isolated  proteins  are  fed  singly,  striking  differences  in 
nutritive  value  appear,  as  has  been  shown  in  Chapter  III.  In 
view  of  this  fact  it  may  seem  strange  that  in  the  experiments 
hitherto  conducted  to  determine  the  protein  requirement  of 
man  the  kind  of  protein  fed  has  not  exerted  a  more  striking 
influence  upon  the  results  obtained.  There  is,  however,  no 
real  discrepancy  between  the  two  sets  of  findings.  The  experi- 
ments described  in  Chapter  III  were  for  the  purpose  of  compar- 
ing individual  proteins  isolated  even  from  the  other  proteins 
which  always  accompany  them  in  natural  or  commercial  food 
materials,  and  were  conducted  largely  upon  rapidly  growing 
young  animals,  in  which  there  is  an  active  synthesis  and  reten- 
tion of  protein,  so  that  a  deficiency  in  the  supply  of  any  amino 
acid  which  is  required  in  the  construction  of  body  protein  is  apt 
to  be  quickly  and  plainly  reflected  in  a  diminution  or  cessation 
of  growth.  On  the  other  hand,  in  experiments  like  those  de- 
scribed in  the  preceding  section,  where  the  purpose  is  not  to 
compare  proteins  but  to  measure  the  normal  protein  require- 
ment, the  diet  is  naturally  made  up,  not  of  isolated  pf-oteins  or 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT      223 

even  of  single  or  unusual  foods,  but  (ordinarily  at  least)  of  such 
combinations  of  staple  foods  as  is  believed  to  represent  a  normal 
diet,  so  that  even  a  relatively  simple  ration  arranged  for  the 
purposes  of  such  an  experiment  would  probably  contain  a  num- 
ber of  different  proteins  among  which  any  pecuHarities  of  amino 
acid  make-up  would  be  apt  to  offset  each  other.  Moreover  the 
experiments  of  the  latter  group  have  been  made  entirely  upon 
adults  whose  protein  requirement  was  Hmited  to  that  of  main- 
tenance. In  such  cases  there  is  no  longer  a  demand  for  amino 
acids  to  be  built  into  new  tissue,  but  only  to  maintain  the  equi- 
librium which  now  exists  between  amino  acids  and  proteins  in 
the  tissues  already  full  grown.  Any  of  the  amino  acids  whose 
radicles  are  contained  in  tissue  proteins  may  be  expected  to 
contribute  something  to  the  maintenance  of  such  an  equiHbrium, 
whereas  there  can  be  no  growth  unless  all  the  necessary  amino 
acids  are  present.  In  a  corresponding  series  of  experiments 
upon  growing  children  or  nursing  mothers  the  influence  of  food 
selection  would  probably  be  much  more  pronounced. 

Even  for  the  maintenance  of  adults  protein  requirement  may  be  found 
to  be  considerably  influenced  by  food  selection  when  experiments  suitably 
planned  to  test  the  question  are  carried  out.  The  inadequacy  of  gelatin  as 
a  sole  protein  food  and  its  inferiority  to  meat  or  milk  protein  when  substi- 
tuted beyond  a  certain  proportion  are  well  known.  A  series  of  experiments, 
designed  to  demonstrate  differences  in  nutritive  efficiency  for  man  of  the 
protein  supplied  by  different  staple  articles  of  food,  was  carried  out  by  Karl 
Thomas  in  Rubner's  laboratory  and  the  striking  results  obtained  have  been 
widely  quoted,  often  on  Rubner's  authority.  These  results,  however,  have- 
as  yet  failed  of  confirmation,  and  on  some  important  points  have  been  so 
directly  refuted  by  later  workers  using  longer  experimental  periods,  as  to 
make  it  appear  that  Thomas's  plan  of  experimenting  and  mode  of  inter- 
pretation were  not  entirely  suited  to  the  solution  of  the  question  at  issue. 

Thomas  1  thought  he  had  demonstrated  that  meat  protein  was  greatly 
superior  to  bread  or  potato  protein  for  the  maintenance  of  body  tissue; 
but  Hindhede  finds  no  such  difference,  being  able  to  maintain  normal  nutri- 
tion with  either  bread  or  potato  nitrogen  in  relatively  small  amounts. 

1  Thomas,  Archiv  Jiir  Anaiomie  und  Physiologic,  1909,  pages  219-302. 


224  CHEMISTRY  OF  FOOD  AND  NUTRITION  \ 

i 

Rose  and  Cooper  *  have  also  demonstrated  the  high  value  of  potato 
nitrogen  in  the  maintenance  of  nitrogen  equilibrium,  and  preliminary  ex- 
periments in  the  writer's  laboratory  f  have  tended  to  confirm  Hindhede's 
finding  that  nitrogen  equilibrium  may  be  maintained  on  a  relatively  low 
intake  of  protein  in  the  form  of  bread. 

Of  greater  practical  importance  than  the  experiments  with  bread  alone 
are  those  f  which  show  the  maintenance  of  nitrogen  equiUbrium  over  long 
periods  on  low  protein  diets  in  which  bread  is  the  chief  source  of  protein, 
but  is  supplemented  by  small  amounts  of  milk. 

Since  estimates  of  protein  requirement,  in  order  to  be  of 
general  application,  should  provide  for  the  needs  of  growth, 
reproduction,  and  lactation,  as  well  as  for  maintenance,  it  will 
be  well  to  consider  more  fully  the  results  obtained  in  feeding 
experimental  animals  upon  known  rations  throughout  the  period 
of  growth  or  the  entire  life  cycle. 

It  will  be  remembered  that  Osborne  and  Mendel,  feeding 
isolated  proteins  in  liberal  proportion  (i8  per  cent)  in  diets 
adequate  and  well  balanced  as  regards  all  other  factors,  found 
that  edestin,  a  typical  vegetable  globulin,  was  able  to  supply  all 
the  protein  requirements  of  maintenance,  reproduction,  and 
growth,  even  through  three  generations  of  rats.  With  gliadin 
as  the  sole  protein,  maintenance  was  satisfactory  but  growth 
was  inhibited ;  but  an  addition  of  lysine  to  this  diet  caused  an 
immediate  resumption  of  growth.  When  the  supply  of  lysine 
was  cut  ojff,  growth  again  ceased.  A  ration  containing  zein  as 
the  sole  protein  did  not  suffice  even  for  maintenance ;  but  when 
tryptophane  was  added  to  it,  or  gliadin,  which  contains  trypto- 
phane, it  served  to  maintain  body  weight,  and  on  further  addition 
of  lysine,  growth  ensued. 

In  order  to  emphasize  such  differences  as  these  it  is  some- 
times thought  advantageous  to  classify  proteins  as : 

A .  Complete :  Capable  of  maintaining  adults  and  providing 
for  normal  growth  of  the  young  when  used  as  a  sole  protein 

*  Rose  and  Cooper,  Journal  of  Biological  Chemistry,  Vol.  30,  pages  201-204. 
t  Not  yet  published. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     225 

food.  Casein  and  lactalbumin  of  milk;  ovalbumin  and  ovo- 
viteUin  of  egg;  glycinin  of  soy  bean;  excelsin  of  Brazil  nut; 
edestin,  glutenin,  and  maize-glutelin  of  the  cereal  grains. 

B.  Partially  Incomplete:  Capable  of  maintaining  life  but 
not  of  supporting  normal  growth.  Gliadin  of  wheat  is  the  well- 
demonstrated  example  of  this  class. 

C.  Incomplete:  Incapable  either  of  maintaining  life  or  of 
supporting  growth,  when  fed  as  the  sole  protein.  Zein  of  corn 
(maize),  and  gelatin  are  the  conspicuous  examples. 

Any  such  grouping  of  the  proteins,  however,  must  be  used 
with  much  discrimination,  and  with  great  care  to  insure  an 
understanding  of  the  quantitative  aspects  of  the  experimental 
data,  if  misconceptions  are  to  be  avoided.  Edestin  is  a  con- 
spicuous example  of  a  "  complete  "  protein,  having  served  as 
above  noted  as  the  sole  protein  food  of  a  family  of  rats  for  three 
generations;  but  when  the  percentage  of  edestin  in  the  food 
mixture  was  considerably  reduced,  results  like  those  above 
described  for  gliadin  were  obtained  — .the  diet  did  not  support 
a  normal  rate  of  growth,  but  this  could  be  secured  by  adding 
lysine  to  the  food  mixture.  Similarly  casein  when  fed  in  reduced 
proportion  to  the  total  food  mixture  did  not  support  normal 
growth;  but  growth  became  normal  when  cystine  was  added. 
Thus  "  complete  "  proteins  may  behave  as  "  partially  incom- 
plete "  when  fed  in  reduced  proportion.  It  is  also  to  be  remem- 
bered that  varying  rates  of  growth  in  different  species  (not 
to  mention  other  differences)  make  inadmissible  any  broad 
generalizations  as  to  the  proportion  in  which  any  protein  should 
be  fed  to  species  other  than  that  with  which  its  "  completeness  " 
or  "  incompleteness  "  has  been  demonstrated. 

In  some  of  their  most  recently  published  experiments  (1916) 
Osborne  and  Mendel  give  quantitative  measurements  of  the 
relative  efficiency  (for  support  of  growth  in  young  rats)  of  some 
of  the  "  complete  "  proteins.  The  rate  of  gain  obtained  with 
8  per  cent  of  lactalbumin  required  12  per  cent  of  casein  or  15 


226  CHEMISTRY  OF  FOOD  AND   NUTRITION 

per  cent  of  edestin ;  or,  as  they  also  state  the  result,  "  to  pro- 
duce the  same  gain  in  body  weight  50  per  cent  more  c§,sein 
than  lactalbumin  was  required,  and  of  edestin  nearly  90  per 
cent  more."  In  maintenance  experiments,  2.4  to  3  per  cent  of 
lactalbumin  was  as  effective  as  3.5  to  4  per  cent  of  casein  or 
edestin. 

On  extending  their  experiments  from  rats  to  chicks,  Osborne 
and  Mendel  again  found  that  proteins  rich  in  lysine  are  much 
more  effective  for  growth  than  those  in  which  the  proportion  of 
lysine  is  much  smaller. 

McCoUum  found  milk  protein  much  more  efficient  than 
wheat  or  maize  protein  in  supporting  the  growth  of  young 
pigs. 

As  in  growth,  so  in  lactation,  the  demand  for  material  for  the 
construction  of  new  protein  creates  a  condition  in  which  differ- 
ences of  value  in  the  protein  fed  may  readily  become  more  ap- 
parent than  when  only  maintenance  is  involved.  Hart  and 
Humphrey  find  that  in  meeting  the  protein  requirements  of 
milch  cows,  milk  protein  and  the  protein  of  flaxseed,  "  oil  meal," 
are  about  50  per  cent  more  efiicient  than  the  proteins  of  the  corn 
(maize)  or  of  the  wheat  kernel;  and  Hoobler  has  shown  that 
milk  is  the  best  form  of  food  protein  for  the  production  of 
human  milk  and  the  protection  of  the  body  protein  of  the  nurs- 
ing mother. 

Influence  of  Muscular  Exercise 

At  one  time  it  was  supposed  that  muscular  power  was  gener- 
ated at  the  expense  of  muscle  substance  and  this,  of  course, 
necessitated  the  belief  that  muscular  work  always  increased  pro- 
tein metaboHsm.  Since  we  now  know  that  the  muscles  work 
quite  as  well  at  the  expense  of  carbohydrates  and  fats  as  of  pro- 
tein, the  conclusion  that  muscular  work  necessarily  increases 
the  metabolism  of  protein  is  -far  from  inevitable.  It  is  only 
necessary  to  observe  the  effects  of  regular  muscular  exercise. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     227 

either  in  athletic  training  or  in  normal  labor,  to  see  that  the 
muscles  do  not  waste  away  when  thus  used,  but  rather  tend  to 
become  larger.  Such  a  growth  of  the  muscles  tends  toward  a 
storage  rather  than  a  loss  of  protein.  Usually,  however,  mus- 
cular work  also  results  in  increased  appetite,  and  it  is  difficult 
to  separate  the  effects  of  the  exercise  from  those  of  the  extra 
food. 

Whether  muscular  work  acts  directly  to  increase  the  amount 
of  protein  metabolized  in  the  body  can  only  be  determined  by 
experiments  in  which  sufficient  extra  fats  and  carbohydrates 
are  fed  to  furnish  the  extra  fuel  required  on  the  working  days. 
But  since  fats  and  carbohydrates  spare  protein,  the  feeding  of 
these  in  any  excess  over  just  what  is  necessary  to  provide  for  the 
increased  energy  requirement  would  tend  to  decrease  the  metab- 
olism of  protein  and  counteract  any  effect  which  the  muscular 
work  might  otherwise  have  in  increasing  protein  metabohsm. 
Hence,  in  order  to  show  conclusively  whether  muscular  work  of 
itself  has  any  influence  upon  the  protein  metabolism,  it  would 
be  necessary  to  determine  the  mechanical  efficiency  of  the  man, 
then  to  bring  him  into  equihbrium  with  an  amount  of  food  just 
sufficient  for  his  needs,  and  finally  to  have  him  perform  a  meas- 
ured amount  of  work  at  the  same  time  adding  to  his  diet  an 
amount  of  fats  and  carbohydrates  just  sufficient  to  furnish  the 
extra  energy  required  for  the  work  performed.  Such  elaborate 
experiments  have  not  yet  been  made,  but  we  have  sufficient 
data  to  show  that  they  are  not  necessary  for  practical  purposes. 
Many  experiments  have  shown  conclusively  that  increased  work, 
when  accompanied  by  a  sufficient  increase  in  the  amount  of  fats 
and  carbohydrates  fed,  does  not  necessarily  increase  the  metab- 
olism of  protein. 

The  following  data  from  Atwater  {Report  of  the  Storrs,  Con- 
necticut, Agricultural  Experiment  Station  for  iQ02-igoj,  page 
127)  show  the  average  results  of  a  long  series  of  rest  and  work 
experiments  with  men  in  the  respiration  calorimeter : 


228  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Muscular  Work  and  Protein  Metabolism  (Atwater) 


Nature  of  Experiment 


Average  Metabolism  per  Day 


Per  Person 


Energy, 
Calories 


Protein 
Grams 


Per  Kilogram 
Body  Weight 


Energy, 
Calories 


Protein, 
Grams 


Per  Square 
Meter  Surface 


Energy, 
Calories 


Protein, 
Grams 


Rest :  Food  generally  sufficient 
for  equilibrium ;  5  subjects, 
27  experiments,  covering  82 
days 


2310 


103.8 


33.5 


I-5I 


16 


50.1 


Work:  8  hours  per  day.  Food 
generally  not  quite  sufficient 
for  equilibrium ;  3  subjects, 
24  experiments,  covering  76 
days 


4556 


108. 1 


62.9 


149 


2129 


So.S 


Comparing  the  figures  either  per  unit  of  weight  or  of  surface, 
it  will  be  seen  that  muscular  work  sufficient  to  nearly  double 
the  energy  metabolism  had  no  appreciable  effect  upon  the 
amount  of  protein  metabolized.  Considering  the  large  amount 
of  exceptionally  accurate  research  represented  in  these 
figures,  they  seem  to  justify  the  conclusion  that  if  muscular 
^ork  has  any  tendency  to  increase  the  "  wear  and  tear  "  of 
muscle  substance,  such  effect  is  normally  balanced  by  the  tend- 
ency of  the  muscles  to  grow  (and  therefore  store  protein)  when 
exercised. 

Moreover,  it  is  certain  that  any  effect  which  muscular  work 
might  possibly  have  in  increasing  protein  metabolism  would  be 
incomparably  less  than  its  effect  in  increasing  the  total  metab- 
ohsm.  If,  then,  starting  with  a  diet  which  maintains  protein 
equilibrium  at  rest,  the  total  food  is  increased  sufl&ciently  to 
provide  for  the  muscular  work,  and  the  increase  in  the  diet  is 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     229 

accomplished  by  adding  any  reasonable  combination  of  food 
materials,  we  may  feel  sure  that  these  will  supply  plenty  of 
protein  to  meet  any  possible  increase  in  the  protein  requirement. 
Hence,  in  planning  the  diet  of  a  man  at  hard  muscular  work, 
any  reasonable  combination  of  foodstuffs  given  in  sufficient 
abundance  to  meet  the  energy  requirement  will  almost  certainly 
supply  an  ample  amount  of  protein. 

Shaffer  has  studied  the  output  of  ammonia,  creatinine,  and 
uric  acid  as  well  as  of  total  nitrogen  during  rest  and  work  and 
finds  no  significant  change  in  any  of  these.  Lusk  considers  it 
fully  proved  that  neither  the  amount  nor  the  character  of  pro^ 
tein  metabolism  is  changed  by  muscular  activity. 

Protein  Requirement  in  Relation  to  Age  and  Growth 

If  a  man  at  moderately  active  work  takes  a  diet  which  fur- 
nishes 3000  Calories  and  75  grams  of  protein,  he  is  taking  10 
per  cent  of  his  calories  in  the  form  of  protein.  Of  course  the 
protein  requirement  cannot  bear  a  fixed  relation  to  the  calorie 
requirement,  since  the  latter  is  largely  influenced  by  activity, 
while  the  former  is  not.  Most  men,  when  at  complete  rest, 
would  require  more  than  10  per  cent  of  their  calories  in  the  form 
of  protein  because  the  lack  of  exercise  would  not  reduce  the 
protein  requirement  to  the  same  extent  as  the  energy  require- 
ment. On  the  other  hand,  most  Americans  are  accustomed  to 
take  more  than  10  per  cent  of  their  calories  as  protein  regardless 
of  whether  they  require  it  or  not.  If,  then,  the  active  man's 
need  for  protein  is  met  by  supplying  him  with  10  per  cent  of 
his  needed  calories  in  the  form  of  protein,  this  will  serve  as  a 
convenient  starting  point  in  considering  the  requirements  of  a 
child.  Let  this  be  compared  with  the  normal  dietary  of  an 
infant.  Human  milk  averages  about  1.6  per  cent  protein,  4.0 
per  cent  fat,  7.0  per  cent  carbohydrate.  Here  about  9  per  cent 
of  the  calories  are  taken  in  the  form  of  protein,  or  about  the 
same  proportion  as  has  been  allowed  for  the  full-grown  active 


230  CHEMISTRY  OF  FOOD  AND  NUTRITION 

man.  Furthermore  Hoobler  has  shown  experimentally  that 
this  is  as  high  a  proportion  of  protein  as  the  infant  will  utiHze 
with  the  highest  efficiency  in  growth  of  body  tissue.  During 
the  suckling  period  the  growth  is  relatively  more  rapid  than  at 
any  other  age.     Mendel  *  gives  the  following  figures : 

The  Relative  Daily  Gain  in  Body  Weight  of  Children 

In  the  first  month  is  about i.oo  per  cent 

At  the  middle  of  the  first  year     . 0.30  per  cent 

At  the  end  of  the  first  year     . 0.15  per  cent 

At  the  fifth  year        0.03  per  cent 

Maximum  in  later  years 

for  boys 0.07  per  cent 

for  girls        0,04  per  cent 

If,  then,  the  full-grown  man  and  the  child  at  the  time  of  most 
rapid  growth  each  requires  but  10  per  cent  of  his  calories  in  the 
form  of  protein,  it  seems  probable  that  this  proportion  is  also 
sufficient  for  any  intermediate  age,  if  the  diet  is  of  ample  fuel 
value,  and  the  protein  is  of  the  right  kind.  But  the  proper 
selection  of  the  protein  is  of  very  great  importance  in  the  feeding 
of  children,  who  differ  from  most  other  young  mammals  in  that 
their  period  of  growth  is  so  many  times  longer  than  the  suckling 
period.  Even  the  child  that  is  nursed  for  a  year  and  attains 
three  times  his  birth-weight  before  weaning  will  still  have  much 
the  greater  part  (probably  five  sixths)  of  his  growth  to  make 
on  other  food.  By  the  time  growth  is  complete  he  will  prob- 
ably have  about  twenty  times  the  body  weight  and  more  than 
twenty  times  the  body  protein  with  which  he  was  born. 

Growth  at  the  normal  rapid  rate  of  early  childhood  involves 
the  conversion  of  a  very  considerable  part,  sometimes  as  much 
as  one  third,  of  the  protein  of  the  food  into  body  protein.  This 
can  be  accompHshed  to  the  best  advantage  only  when  (i)  the 
protein  of  the  food  is  largely  of  the  kind  most  efficient  in  sup- 
porting growth, i.e.  milk  protein;  (2)  the  protein  is  well  "  pro- 

*  Childhood  and  Growth,  p.  18. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT     231 

tected  "  by  the  protein-sparing  action  of  liberal  amounts  of 
carbohydrate  and  fat. 

That  the  child  needs  a  diet  of  high  fuel  value  to  meet  the 
requirements  of  his  energy  metabolism  has  already  been  pointed 
out  (Chapter  VII).  It  is  because  the  high  protein  requirement 
of  childhood  (for  young  children  more  than  twice  as  much  per 
unit  of  weight  as  for  adults)  is  paralleled  by  an  equally  high 
energy  requirement  that  the  diet  of  the  child  need  not  contain 
a  higher  percentage  of  its  calories  in  the  form  of  protein  than 
does  the  ordinary  diet  of  the  adult,  if  the  protein  for  the  child 
is  well  chosen. 

Usually,  however,  a  well-planned  dietary  for  a  child  will  show 
a  somewhat  more  than  average  proportion  of  its  calories  in  the 
form  of  protein  because  after  weaning  the  main  feature  of  the 
child's  diet  should  be  cows'  milk  which  furnishes  about  19  per 
cent  of  its  calories  in  the  form  of  protein.  A  child,  fed  mainly 
upon  cows'  milk  and  taking  enough  food  to  amply  cover  his 
energy  requirement,  will  therefore  receive  a  safe  surplus  of  pro- 
tein in  the  best  available  form.  With  a  full  quart  of  milk  in 
the  daily  dietary  of  the  growing  child  the  other  foods  may  be 
selected  chiefly  with  reference  to  other  qualities  than  their  pro- 
tein content;  without  a  liberal  use  of  milk  the  proper  feeding 
of  a  growing  child  becomes  a  very  difficult  problem. 

Having  discussed  the  protein  requirements  of  ordinary  adult 
maintenance  and  of  growth,  the  requirements  of  the  aged  should 
also  be  considered.  This  does  not  require  extended  discussion, 
since  advancing  age  involves  no  new  features  but  only  a  gradual 
modification  of  those  pertaining  to  middle  life. 

In  general,  elderly  people  show  a  somewhat  diminished  pro- 
tein requirement  and  likewise  a  diminished  power  of  dealing 
with  excess.  Surplus  protein  taken  in  the  food  is  not  so  rapidly 
absorbed  and  catabolized,  and,  while  there  appears  to  be  no 
essential  difference  in  the  form  in  which  the  nitrogen  is  finally 
excreted,  the  susceptibility  to  excessive  putrefaction  of  protein 


232  CHEMISTRY  OF  FOOD  AND  NUTRITION 

appears  to  be  increased.  It  would  seem  that  in  the  dietary  of 
the  a^ed  the  protein  should  be  reduced  to  at  least  as  great  an 
extent  as  are  the  calories. 


REFERENCES 

Atwater  and  Benedict.  Comparison  of  Fats  and  Carbohydrates  as 
Protectors  of  Body  Material.  Bulletin  136  (pages  176-187),  OflSce 
of  Experiment  Stations,  U.  S.  Dept.  Agriculture. 

Benedict.  The  Influence  of  Inanition  on  Metabolism  (Publication  77) 
and  A  Study  of  Prolonged  Fasting  (Publication  203).  Carnegie  Insti- 
tution of  Washington. 

Cathcart.    Physiology  of  Protein  Metabolism. 

Chittenden.    Physiological  Economy  in  Nutrition. 

Chittenden.    The  Nutrition  of  Man. 

Hart  and  Humphrey.  The  Relation  of  the  Quality  of  Proteins  to  Milk 
Production.  Journal  of  Biological  Chemistry,  Vol.  21,  page  239  (1915); 
Vol.  26,  page  457  (1916) ;  Vol.  31,  page  445  (iQi?)- 

Hindhede.     Protein  and  Nutrition. 

HiNDHEDE.  Nutritive  Value  of  the  Proteins  of  Potatoes  and  of  Bread. 
Skandinavisches  Archiv  f.  Physiologie,  Vol.  30,  page  97  (1913) ;  Vol.  31, 
page  259  (1914). 

HooBLER.  The  Protein  Need  of  Infants.  American  Journal  of  Diseases 
of  Children,  Vol.  10,  page  153  (1915). 

HooBLER.  The  Effect  on  Human  Milk  Production  of  Diets  Containing 
Various  Forms  and  Quantities  of  Protein.  American  Journal  of  Dis- 
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Association,  Vol.  69,  page  421  (August,  1917). 

LusK.     Elements  of  the  Science  of  Nutrition. 

McCoLLUM.  The  Nature  of  the  Repair  Processes  in  Protein  Metabolism. 
American  Journal  of  Physiology,  Vol.. 29,  page  215  (191 2). 

McCoLLUM.  The  Value  of  the  Proteins  of  Cereal  Grains  and  of  Milk,  for 
Growth  in  the  Pig.  Journal  of  Biological  Chemistry,  Vol.  19,  page  323 
(1914). 

McCoLLUM  and  Davis.  Influence  of  the  Plane  of  Protein  Intake  on  Growth. 
Journal  of  Biological  Chemistry,  Vol.  20,  page  415  (1915)- 

McCoLLUM,  SiMMONDS,  AND  PiTZ.  Effccts  of  Feeding  the  Proteins  of  the 
Wheat  Kernel  at  Different  Planes  of  Intake.  Journal  of  Biological 
Chemistry,  Vol.  28,  page  211  (1916). 

McKay.    The  Protein  Element  in  Nutrition. 


FACTORS  DETERMINING  PROTEIN  REQUIREMENT      233 

Mendel.  Nutrition  and  Growth.  Harvey  Society  Lectures,  1914-1915,  and 
Journal  of  the  American  Medical  Association,  Vol^4,  page  1539  (1914). 

MuRLiN.  The  Nutritive  Value  of  Gelatin.  Ameruan  Journal  of  Physi- 
ology, Vol.  19,  page  285;  Vol.  20,  page  234  (1907-1908). 

MuRLiN  AND  Bailey.  Protein  Metabolism  in  Normal  Pregnancy.  Ar- 
chives of  Internal  Medicine,  Vol.  12,  page  288  (1913). 

Osborne  and  Mendel.  (A  Series  of  papers  upon  the  nutritive  functions 
and  relative  efficiency  of  individual  proteins  and  amino  acids  in  main- 
tenance and  growth.)  Journal  of  Biological  Chemistry,  Vol.  1 2,  page  473 ; 
Vol.  13,  page  233  (1912);  Vol.  17,  page  325;  Vol.  18,  page  i  (1914); 
Vol.  20,  page  351 ;  Vol.  22,  page  241  (1915) ;  Vol.  25,  page  i ;  Vol.  26, 
pages  I,  293  (1916).  (Subsequent  issues  should  also  be  consulted  for 
papers  appearing  after  the  compilation  of  this  list.) 

Rose  and  Cooper.  The  Biological  Efficiency  of  Potato  Nitrogen.  Jour- 
nal of  Biological  Chemistry,  Vol.  30,  page  201  (191 7). 

SiVEN.  (Experiments  on  Protein  Requirement.)  Skandinavisches  Archiv  f. 
Physiologic,  Vol.  10,  page  91;  Vol.  11,  page  308. 

VoN  NooRDEN.     Metabolism  and  Practical  Medicine,  Vol.  i,  pages  283-383. ' 

Wilson.  Nitrogen  Metabolism  during  Pregnancy.  Bulletin  of  the  Johns 
Hopkins  Hospital,  Vol.  27,  page  121  (1916). 


CHAPTER  IX 

INORGANIC   FOODSTUFFS   AND   THE   MINERAL 
METABOLISM 

The  Elementary  Composition  of  the  Body 

From  various  estimates  by  different  writers  the  average  ele- 
mentary composition  of  the  human  body  may  be  presumed  to 
be  approximately  as  follows : 

Oxygen,  about 65.  per  cent 

Carbon,  about 18.  per  cent 

Hydrogen,  about       . 10.  per  cent 

Nitrogen,  about 3-  per  cent 

Calcium,  about 2.  per  cent 

Phosphorus,  about i.  per  cent 

Potassium,  about 0.35  per  cent 

Sulphur,  about 0.25  per  cent 

Sodium,  about 0.15  per  cent 

Chlorine,  about 0.15  per  cent 

Magnesium,  about 0.05  per  cent 

Iron,  about 0.004  per  cent 

Iodine     1  f  Very- 
Fluorine  > \  minute 

Silicon     J  [  quantities 

Traces  of  some  other  elements  such  as  manganese  and  alumin- 
ium may  perhaps  be  normal  constituents  of  the  body  also,  and 
even  arsenic  has  been  discussed  as  a  possible  essential  element. 
In  this  book  only  those  elements  are  discussed  of  which  the 
amounts  concerned  in  daily  metaboHsm  can  be  measured  quan- 
titatively by  present  methods. 

Since  all  of  the  substances  in  the  body  are  continually  under- 
going disintegration  and  renewal,  it  follows  that  there  must  be 

234 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      235 

a  constant  metabolism  or  exchange  of  every  element  which  enters 
into  body  structure.  More  or  less  of  each  element  must  each 
day  be  metabolized  and  eHminated ;  and,  if  equiUbrium  is  to  be 
maintained,  an  equal  amount  must  be  supplied. 

Simple  proteins  furnish  only  five  of  the  fifteen  chemical  ele- 
ments which  are  known  to  be  essential  to  human  nutrition, 
while  fats  and  carbohydrates  are  composed  of  but  three  of  these 
five.  Ten  of  the  fifteen  essential  elements,  or  seven  of  the 
twelve  which  are  essential  in  amounts  sufficiently  large  to  be 
measurable  by  present  methods,  must  therefore  be  furnished 
by  some  ingredients  of  the  intake  other  than  simple  proteins, 
fats,  and  carbohydrates.  These  same  elements  are  found  to 
remain  either  wholly  or  largely  in  the  ash  of  food  materials  when 
the  latter  are  burned  in  the  air ;  and  when  the  food  is  metab- 
olized in  the  body  they  are  excreted  chiefly  in  the  form  of 
mineral  matter.  These  elements  are  therefore  grouped  as  "  ash 
constituents,"  "  minerals,"  "  mineral  salts,"  "  inorganic  ele- 
ments," or  "  the  inorganic  foodstuffs  " ;  and  their  metaboHsm 
is  commonly  designated  as  ''  the  mineral  metaboHsm."  None 
of  these  terms  is  entirely  appropriate.  To  designate  the  ele- 
ments which  remain  in  the  ash  when  food  is  burned  as  ash  con- 
stituents is  accurate  but  not  very  instructive,  since  the  materials 
of  which  a  food  ash  is  composed  may  have  existed  in  quite  dif- 
ferent forms  of  combination  in  the  food  before  it  was  burned. 
The  terms  "  mineral  "  and  "  inorganic  "  are  likely  to  be  some- 
what misleading.  Some  of  the  elements  (as  sodium  and  chlo- 
rine) do  exist  in  the  food  and  enter  and  leave  the  body  in  in- 
organic forms;  others  (as  iron  and  sulphur)  exist  in  the  food 
and  function  in  nutrition  as  essential  constituents  of  organic 
matter  and  become  inorganic  only  as  the  organic  matter  is  oxi- 
dized, i.e.  only  in  the  late  stages  of  their  metabolism;  still 
others  (as  phosphorus)  are  supplied  to  the  body  by  the  food  in 
both  organic  and  inorganic  forms. 

The  elements  concerned  in  "  the  mineral  metabolism  "  may 


236  CHEMISTRY  OF  FOOD  AND  NUTRITION 

exist  in  the  body  and  take  part  in  its  functions  in  at  least  three 
kinds  of  ways: 

(i)  As  bone  constituents,  giving  rigidity  and  relative  per- 
manence to  the  skeletal  tissues. 

(2)  As  essential  elements  of  the  organic  compounds  which 
are  the  chief  solid  constituents  of  the  soft  tissues  (muscles, 
blood  cells,  etc.). 

(3)  As  soluble  salts  (electrolytes)  held  in  solution  in  the  fluids 
of  the  body,  giving  these  fluids  their  characteristic  influence 
upon  the  elasticity  and  irritability  of  muscle  and  nerve,  supply- 
ing the  material  for  the  acidity  or  alkalinity  of  the  digestive 
juices  and  other  secretions,  and  yet  maintaining  the  neutrality 
or  slight  alkalescence  of  the  internal  fluids  as  well  as  their 
osmotic  pressure  and  solvent  power. 

A  man  under  average  conditipns  of  diet,  activity,  and  health 
usually  excretes  daily  from  20  to  30  grams  of  mineral  salts, 
consisting  essentially  of  chlorides,  sulphates,  and  phosphates  of 
sodium,  potassium,  magnesium,  and  calcium  (as  well  as  am- 
monium salts  from  the  protein  metaboHsm). 

The  purpose  of  this  chapter  and  the  one  following  is  to 
sketch  briefly  the  metabolism  of  these  substances,  with  a 
more  detailed  quantitative  study  of  the  three  elements  (cal- 
cium, phosphorus,  and  iron)  which  assume  an  especial  promi- 
nence in  the  practical  problems  of  nutrition. 

Metabolism  of  Chlorides  —  Use  of  Common  Salt 

Except  for  the  hydrochloric  acid  of  the  gastric  juice,  prac- 
tically all  the  chlorine  involved  in  metaboUsm  enters,  exists  in, 
and  leaves  the  body  in  the  form  of  chlorides  —  much  the  greater 
part  as  sodium  chloride.  The  amount  of  sodium  chloride  which 
is  ordinarily  added  to  food  as  a  condiment  is  so  large  that  the 
amounts  of  sodium  and  chlorine  present  in  the  various  foods  in 
the  fresh  state  become  of  httle  practical  consequence.  Among 
animals  the  herbivora  require  salt  while  the  carnivora  do  not, 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      237 

the  latter  obtaining  sufficient  salt  for  their  needs  from  the  flesh, 
and  more  especially  from  the  blood,  of  their  prey. 

Sodium  occurs,  chiefly  as  chloride,  abundantly  in  the  blood 
and  other  fluids  of  the  animal  body  and  in  much  lower  concen- 
tration in  the  tissues.  Potassium,  on  the  other  hand,  occurs 
to  a  greater  extent  as  phpsphate  than  as  chloride.  It  is  most 
abundant  in  the  soft  solid  tissues  —  in  the  corpuscles  of  the 
blood,  the  protoplasm  of  the  muscles,  and  other  organs,  and 
also  in  the  highly  specialized  fluids  which  some  of  the  glandular 
organs  secrete,  notably  in  milk.  Since  the  cells  are  in  constant 
contact  with  the  circulating  fluids,  the  abundance  of  potassium 
in  the  cells  and  of  sodium  in  the  fluids  makes  it  evident  that 
the  taking  up  of  salts  by  the  cells  is  an  active  or  "  selective  " 
process.  A  conspicuous  function  of  the  salts  in  the  tissues  is 
the  maintenance  of  the  nopnal  osmotic  pressure,  but  solu- 
tions of  different  salts  of  equal  osmotic  pressure  are  by  no 
means  interchangeable,  and  it  is  not  possible  to  replace  suc- 
cessfully the  potassium  in  the  cell  by  an  equivalent  amount 
of  sodium. 

There  seems  to  be  a  relation  between  the  taking  up  of  salt 
and  the  retention  of  water  in  the  tissues.  The  effect  of  decreas- 
ing the  salt  in  the  diet  is  to  decrease  the  quantity  of  salt  in  the 
tissues,  and  at  the  same  time  their  water  content.  An  explana- 
tion of  this  lies  in  the  fact  that,  since  body  tissues  and  fluids 
must  maintain  a  constant  concentration  of  sodium  chloride,  a 
reduction  in  the  absolute  quantity  of  salt  must  result  in  a  cor- 
responding reduction  in  the  quantity  of  water  present. 

Attention  is  frequently  called  to  the  fact  that  sodium  chloride 
is  the  only  salt  which  we  seem  to  crave  in  greater  quantities 
than  occur  naturally  in  our  food,  and  that  we  share  this  appetite 
with  the  herbivorous  animals.  Bunge  holds  that  this  is  because 
a  high  intake  of  potassium  (as  in  most  vegetable  foods)  tends 
to  increase  sodium  ehmination.  Bunge  tested  this  theory  upon 
his  own  person  by  taking  18  grams  of  potash  (as  phosphate  and 


23&  CHEMISTRY  OF  FOOD  AND  NUTRITION 

citrate)  in  one  day.  This  increased  the  eUmination  of  sodium 
chloride  by  6  grams. 

In  his  Physiological  and  Pathological  Chemistry  (Chapter 
VII),  Bunge  records  extended  and  interesting  observations  and 
discussion  upon  the  relation  of  diet  to  the  craving  for  salt,  and 
concludes  that  while  one  might  live  without  the  addition  of 
salt  to  the  food  even  on  a  diet  largely  vegetarian,  yet  without 
salt  we  should  have  a  strong  disincKnation  to  eat  much  of  the 
vegetables  rich  in  potassium,  such  as  potatoes.  "  The  use  of 
salt  enables  us  to  employ  a  greater  variety  of  the  earth's  prod- 
ucts as  food  than  we  could  do  without  it."  But  also,  accord- 
ing to  Bunge :  ''  We  are  accustomed  to  take  far  too  much  salt 
with  our  viands.  Salt  is  not  only  an  aliment,  it  is  also  a  condi- 
ment, and  easily  lends  itself,  as  all  such  things  do,  to  abuse." 
While  Bunge's  explanations  may  not  be  entirely  adequate  in 
detail,  there  seems  to  be  httle  doubt  as  to  the  correctness  of  his 
main  deductions. 

Since  the  sodium  chloride  taken  with  the  food  passes  through 
the  body  and  is  excreted  by  the  kidneys  without  undergoing 
any  chemical  change,  the  rate  of  excretion  quickly  adapts  itself 
to  the  rate  of  intake  within  wide  variations. 

When  no  chloride  is  taken,  the  rate  of  excretion  falls  rapidly 
to  a  point  where  the  daily  loss  is  only  a  very  small  fraction  of 
the  amount  ordinarily  consumed  and  excreted.  Thus  in  an 
experiment  by  Goodall  and  Joslin  *  in  which  a  healthy  man 
was  placed  upon  a  diet  adequate  in  protein  and  energy  value 
but  practically  free  from  salt,  the  excretion  of  chlorine  on  each 
of  13  successive  days  was  respectively:  4.60,  2.52,  1.88,  0.87, 
0.69,  0.48,  0.46,  0.40,  0.26,  0.22,  0.22,  0.17,  0.17  grams. 

Cetti  in  ten  days  of  fasting  excreted  all  together  13.13  grams, 
and  Belli  in  ten  days  on  a  diet  poor  in  salt  lost  11.8  grams  of 
sodium  chloride.     In  Benedict's  recent  study  of  prolonged  fast- 

*  Goodall  and  Joslin,  Transactions  of  the  Association  of  American  Physicians, 
Vol.  23,  page  92  (1908). 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      239 

ing  *  his  subject  lost  8.44  grams  of  chlorine  (equivalent  to  13.93 
grams  sodium  chloride)  during  the  first  ten  days,  2.13  grams 
chlorine  during  the  second  ten  days,  and  1.57  grams  chlorine 
during  the  third  ten  days  of  the  fast.  (The  detailed  data  may 
be  found  on  a  later  page.)  Since  the  body  is  supposed  to  con- 
tain about  100  grams  of  sodium  chloride,  it  will  be  seen  that 
even  when  there  was  complete  deprivation  of  salt  for  ten  to 
thirty  days,  the  total  losses  did  not  exceed  10  to  20  per  cent  of 
the  amount  estimated  as  usually  present  in  the  body.  The 
salt  thus  readily  given  off  by  the  body  has  been  regarded  by 
some  as  a  measure  of  the  excess  which  the  body  has  been  forced 
to  carry  in  consequence  of  the  extravagant  amounts  of  salt 
which  are  commonly  taken  with  the  food.  Magnus-Levy,  how- 
ever, thinks  that  the  reduced  amount  of  sodium  chloride  left  in 
the  body  after  such  a  loss  is  "  not  a  physiological  optimum,  but 
rather  a  physiological  minimum." 

Moderate  variations  in  the  amount  of  salt  taken  have  no 
significant  effect  upon  metabolism.  Large  amounts  increase  the 
quantity  of  protein  catabolized,  and,  through  overstimulating 
the  digestive  tract,  may  also  interfere  with  the  absorption  and 
utiUzation  of  the  food. 

Metabolism  of  Sulphur 

Plants  absorb  sulphates  from  the  soil  and  use  the  sulphur  in 
the  synthesis  of  proteins.  Minute  quantities  of  inorganic  sul- 
phates may  be  taken  by  man  in  food  and  drink,  but  by  far  the 
greater  part  of  the  sulphur  concerned  in  metabolism  enters  the 
body  in  organic  combination  and,  so  far  as  known,  chiefly  as 
protein.  The  metaboHsm  of  sulphur  is  therefore  a  part  of  the 
protein  metabolism,  and  in  many  respects  the  metabolism  of 
sulphur  tends  to  run  parallel  with  that  of  nitrogen.  In  a 
series  of  ten  experiments  (each  of  3  to  5  days'  duration)  upon 

*  Benedict,  Publication  No.  203,  Carnegie  Institution  of  Washington. 


240 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


man,*  in  which  the  food  consisted  of  bread  and  milk  in  varying 
amounts  and  proportions,  the  percentage  absorption  from  the 
digestive  tract  was  nearly  the  same  for  the  sulphur  as  for  the 
nitrogen  of  the  food,  and  the  excretion  of  the  end  products  ran 
so  closely  parallel  that  in  every  case  in  which  the  body  stored 
nitrogen  it  also  stored  sulphur,  and  vice  versa. t 

It  is  well  known  that  individual  proteins  show  relatively 
much  greater  differences  in  sulphur  than  in  nitrogen  content,  so 
the  ratio  of  nitrogen  to  sulphur  varies  widely,  as  is  shown  by 
the  following  examples  selected  from  the  data  for  pure  proteins 
compiled  by  Osborne : 


Kind  or  Protein 

Nitrogen 
Per  Cent 

Sulphur 
Per  Cent 

Ratio  of  Nitro- 
gen TO  Sulphur 

Legumin 

Zein 

Edestin 

Gliadin 

Leucosin 

Casein 

Myosin 

Serum  globulin    .... 
Egg  albumin 

18.04 
16.13 
18.69 
17.66 
16.80 
15-78 
16.67 
15.85 
15.51 

0.385 

0.600 

0.88 

1.027 

1.280 

0.80 

1.27 

I. II 

1.616 

46.9 :  I 
26.9 :  I 
21.2:  I 
17.2:  I 
13.1:1 
19.7:1 

13.1:1 

14.3 :  I 

9.6:  I 

Thus,  while  many  proteins  approximate  the  usually  assumed 
average  of  16  per  cent  nitrogen  and  i  per  cent  sulphur,  there 
are  considerable  deviations  from  this  ratio  in  both  directions. 

Under  ordinary  conditions,  however,  no  protein  is  eaten  in  a 
pure  state,  but  only  as  the  material  containing  it  is  used  as  an 
article  of  food.  It  is  therefore  the  proportion  of  sulphur  to  the 
total  protein  of  the  food  which  determines  the  ratio  of  sulphur 
to  nitrogen  available  for  nutrition. 

*  Bulletin  121,  Office  of  Experiment  Stations,  U.  S.  Department  of  Agriculture. 
t  Exceptions  to  such  parallelism  of  nitrogen  and  sulphur  balances  have,  however, 
been  reported  in  certain  pathological  conditions. 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      241 

The  proportion  of  sulphur  to  total  protein  has  been  deter- 
mined in  most  staple  foods,  of  which  the  following  are  repre- 
sentative :  * 


Food  Material 

Sulphur  in  Percentage  of 
Total  Protein 

•  Lean  beef  . 

0.95-1.00 
1.4 

0.95-1.09 

1.15-1.29 

1.30 

1.55 
0.69-1.00 
0.80-0.94 

1.07 

Eggs     . 

Milk     .' 

Wheat  flour,  crackers 

Entire  wheat 

Oatmeal 

Beans 

Peas 

Potatoes    . 

Taking  these  figures  as  typical,  it  would  appear  that  in  those 
staple  foods  which  contribute  the  greater  part  of  the  protein  of 
the  diet,  the  ratio  of  protein  to  sulphur  does  not  differ  greatly, 
and  that  in  most  cases  of  ordinary  mixed  diet  there  would  be 
consumed  not  far  from  i  gram  of  sulphur  in  each  100  grams  of 
protein.  We  may  therefore  expect  that  in  health  and  on  an 
ordinary  diet  the  sulphur  requirement  will  usually  be  covered 
when  the  protein  supply  is  adequate. 

When  proteins  (or  their  cleavage  products)  are  oxidized  in 
the  body,  the  sulphur  becomes  converted  for  the  most  part  into 
sulphuric  acid,  which,  of  course,  must  be  neutrahzed  as  rapidly 
as  it  is  formed.  The  greater  part  of  the  sulphuric  acid  formed 
in  metabolism  appears  in  the  urine  as  inorganic  sulphates;  a 
smaller  part  is  found  combined  with  organic  radicles  in  the  form 
commonly  known  as  "  ethereal  "  or  "  conjugated  "  sulphates. 
The  amount  of  ethereal  sulphate  or  the  ratio  of  ethereal  to  in- 
organic sulphate  is  quite  variable,  depending  mainly  upon  the 

*  In  the  data  here  given,  nitrogen  and  sulphur  were  determined  in  the  same 
specimens.     Average  percentages  of  protein  and  sulphur  in  nearly  all  important 
food  materials  may  be  found  in  Tables  I  and  II,  respectively,  of  the  Appendix. 
R 


242  CHEMISTRY  OF  FOOD  AND   NUTRITION 

amount  and  character  of  the  intestinal  putrefaction,  which  in 
turn  is  apt  to  be  considerably  influenced  by  the  food.  On  ordi- 
nary mixed  diet  about  one  tenth  or  one  twelfth  of  the  sulphate 
sulphur  in  the  urine  ordinarily  appears  as  ethereal  sulphates; 
but  when  the  meat  in  the  diet  is  replaced  by  milk,  the  putre- 
faction is  usually  lessened  and  the  proportion  of  ethereal  sul- 
phates lowered.  In  one  case  of  a  healthy  man  who  had  been 
on  a  bread  and  milk  diet  for  a  week,  only  one  thirtieth  of  the 
sulphate  sulphur  was  in  the  form  of  ethereal  sulphates. 

Not  all  of  the  metabolized  sulphur  is  ehminated  as  mineral 
or  "  ethereal  "  sulphate ;  a  part  is  given  off  in  less  completely 
oxidized  forms.  This  "  unoxidized  "  or  "  neutral  "  sulphur 
usually  constitutes  in  healthy  persons  on  full  diet  from  5  to  15 
per  cent  of  the  total  sulphur  eliminated.  In  Folin's  experiment 
upon  very  low  protein  diet,  although  the  total  sulphur  metab- 
oUsm  was  markedly  decreased,  the  quantity  of  neutral  sulphur 
excreted  remained  about  constant,  so  that  the  relative  proportion 
of  sulphur  appearing  in  this  form  was  increased. 

Metabolism  of  Phosphorus 

Phosphorus  compounds  are  as  widely  distributed  in  the  body 
and  as  strictly  essential  to  every  Hving  cell  as  are  proteins. 

Phosphates  are  constantly  excreted  from  the  body  even  after 
long  fasting.  During  a  fast  the  rate  of  excretion  of  phosphates 
does  not  fall  off  rapidly  like  that  of  chlorides,  but  tends  to  run 
more  nearly  parallel  with  the  nitrogen  excretion,  as  would  be 
expected  in  view  of  the  fact  that  the  phosphates  of  the  urine 
represent  not  only  an  excretion  of  preexistent  salts,  but  also  the 
result  of  the  metaboHsm  of  body  tissue. 

Some  of  the  relations  of  the  phosphorus  compounds  to  nutri- 
tional functions  are  outlined  by  Forbes  and  Keith  as  follows : 

"  Among  the  several  inorganic  elements  involved  in  animal 
life  phosphorus  is  of  especial  interest.  No  other  one  enters 
into  such  a  diversity  of  compounds  and  plays  an  important 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      243 

part  in  so  many  functions.  Structurally,  it  is  important  as  a 
constituent  of  every  cell  nucleus  and  so  of  all  cellular  structures ; 
it  is  also  prominent  in  the  skeleton,  in  milk,  in  sexual  elements, 
glandular  tissue,  and  the  nervous  system.  Functionally,  it  is 
involved  in  all  cell  multipHcation,  in  the  activation  and  control 
of  enzyme  actions,  in  the  maintenance  of  neutrality  in  the 
organism,  in  the  conduct  of  nerve  stimuli,  and  through  its  rela- 
tion to  osmotic  pressure,  surface  tension,  and  imbibation  of 
water  by  colloids  it  has  to  do  with  the  movement  of  liquids, 
with  the  maintenance  of  proper  Hquid  contents  of  the  tissues, 
with  cell  movements,  and  with  absorption  and  secretion" 
(Ohio  Agricultural  Experiment  Station,  Technical  Bulletin  No. 
5,  page  11). 

While  the  phosphorus  compounds  of  the  body  and  of  the  food 
are  very  numerous  and  might  be  classified  differently  according 
to  the  standpoint  from  which  they  are  being  considered,  it  will 
be  convenient  for  our  present  purposes  to  divide  them  into  four 
main  groups : 

1.  Inorganic  phosphates,  of  which  potassium  phosphate  is 
probably  the  most  abundant  in  food  and  in  the  fluids  and  soft 
tissues  of  the  body,  while  calcium  phosphate  is  the  chief  inorganic 
constituent  of  bones. 

2.  Phosphorus-containing  proteins,  including  the  nucleo- 
proteins  of  cell  nuclei,  the  lecitho-proteins,  and  the  true  phos- 
phoproteins  such  as  casein  or  caseinogen  of  milk  and  ovovitellin 
of  egg  yolk. 

3.  Phosphatids,  phospholipins  or  phosphorized  fats  —  includ- 
ing lecithins,  lecithans,  kephalins,  etc.  —  which  occur  in  large 
quantity  in  brain  and  nerve  tissue  and  in  smaller  concentra- 
tion (but  probably  as  essential  components)  in  all  the  cells  and 
tissues  of  the  body,  not  only  of  man,  but  of  plants  and  animals 
generally.  The  phosphatids  are  therefore  widely  distributed  in 
food  materials,  but  are  found  in  extremely  varying  proportions 
in  foods  of  different  types.     Egg  yolks  are  conspicuously  rich 


244  CHEMISTRY  OF  FOOD  AND  NUTRITION 

in  phosphatids,  about  two  thirds  of  the  phosphorus  of  the  egg 
being  present  in  this  form. 

4.  Phosphoric  acid  esters  of  carbohydrates  and  related  sub- 
stances such  as  inositol  {"  inosite  ")  and  the  natural  salts  of 
such  esters.  The  calcium,  magnesium,  and  potassium  salts  of 
"  phytic  acid,"  *  collectively  known  as  phytates,  phytins,  or 
phytin,  have  for  some  years  been  regarded  as  the  most  abundant 
phosphorus  compounds  of  the  wheat  kernel  and  probably  of 
the  grains  and  legumes  generally,  if  not  of  all  vegetable  foods. 
Recent  investigations  indicate,  however,  that  not  all  the  phos- 
phorus compounds  which  were  supposed  to  be  phytins  are  really 
salts  of  phytic  acid.  As  has  been  explained  in  Chapter  I,  the 
recent  work  of  Northrup  and  Nelson  indicates  that  starch  con- 
tains phosphorus  as  an  essential  constituent,  and  there  are  other 
indications  of  phosphorus-containing  carbohydrates  or  carbo- 
hydrate-phosphoric acid  esters  in  food  materials  and  also  of  the 
formation  of  hexose-phosphoric  acid  esters  in  the  body  in  the 
course  of  the  carbohydrate  metabolism. 

Thus  we  may  think  of  the  phosphorus  with  which  we  have 
to  deal  in  food  and  nutrition  as  being  partly  in  the  form  of  in- 
organic phosphates  and  partly  in  combination  with  (or  present 
as  a  constituent  of)  each  of  the  three  groups  of  organic  food- 
stuffs—  proteins,  fats,  and  carbohydrates,  or  closely  related 
substances. 

In  the  course  of  digestion  and  metabolism  the  phosphoric 
acid  radicles  are  split  off  from  the  organic  radicles  and  ulti- 
mately nearly  all  of  the  phosphorus  leaves  the  body  as  inorganic 
phosphate.  To  what  extent  the  cleavage  of  the  organic  phos- 
phorus compounds  occurs  in  the  digestive  tract  under  ordinary 
conditions  and  to  what  extent,  if  at  all,  the  phosphorus  of  phos- 
phoproteins  or  phosphatids,  for  example,  is  absorbed  in  organic 
form  is  still  a  subject  of  investigation. 

*  Phytic  acid  is  probably  inositol-hexa-orthophosphoric  acid,  CeHj^OMPe  (Rob- 
inson and  Mueller). 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      245 

Interrelations  of  Phosphates,  Phosphoproteins,  and 
Phosphatids 

Phosphates,  nucleoproteins,  and  phosphatids  are  all  promi- 
nent as  body  constituents. 

The  insoluble  phosphates  constitute  the  chief  mineral  matter 
of  bone ;  while  soluble  phosphates  are  essential  constituents  of 
the  blood  and  protoplasm.  It  is  largely  to  the  presence  of  the 
phosphates  that  the  blood  and  protoplasm  owe  their  ability  to 
remain  neutral  or  faintly  alkahne,  notwithstanding  the  constant 
production  of  acid  in  metabolism,  as  will  be  seen  in  connection 
with  the  discussion  of  the  maintenance  of  neutrality  below. 

The  nucleoproteins  as  constituents  of  cell  nuclei  and  the  phos- 
phatids as  prominent  constituents  of  brain  and  nerve  tissue  and 
as  less  prominent  but  doubtless  essential  components  of  the 
tissues  generally  have  functions  distinct  from  each  other  and 
from  the  phosphates.  On  the  assumption  of  a  more  active 
metabolism  in  the  cell  nuclei  or  in  the  brain  and  nerve  tissue 
than  in  the  bones,  there  has  sometimes  been  a  tendency  to  regard 
fluctuations  of  phosphorus  output  as  indicative  of  increased  or 
decreased  metabolism  of  nucleoproteins  or  phosphatids.  It  is 
probable,  however,  that  the  eliminated  phosphorus  represents 
more  largely  material  which  has  functioned  as  phosphate.  One 
reason  for  this  is  that  the  bones  contain  so  large  a  share  of  the 
total  phosphorus  of  the  body.  According  to  Voit's  estimate,  a 
man's  skeleton  contains  about  600  grams  of  phosphorus;  his 
muscles,  about  56  grams ;  his  brain  and  nerves,  about  5  grams. 
With  the  bones  in  possession  of  such  a  predominant  share  of 
the  body  phosphorus,  it  would  seem  that  the  metabohsm  of 
bone  tissue,  even  though  relatively  inactive,  must  exert  a  con- 
siderable influence  upon  the  phosphorus  output.  Moreover, 
the  soluble  phosphates  of  the  blood  and  protoplasm  are  con- 
stantly tending  to  be  eHminated  from  the  body  (through  the 
kidneys  or  the  intestinal  walls  or  both)  and  perhaps  increasingly 


246  CHEMISTRY  OF  FOOD  AND   NUTRITION 

SO  in  proportion  as  they  become  changed  into  acid  phosphates 
in  the  performance  of  their  function  of  maintaining  neutrality 
by  reacting  with  the  acids  produced  in  metabolism.  Before 
taking  up  the  quantitative  study  of  the  phosphorus  requirement 
we  must  consider  the  nutritive  relations  of  the  different  types 
of  phosphorus  compounds,  and  whether  these  are  sufficiently 
interchangeable  in  nutritive  function  so  that  one  may  properly 
speak  of  phosphorus  requirement,  simply,  without  discriminating 
between  phosphates,  phytates,  phosphoproteins,  andphosphatids. 

Such  experimental  evidence  as  is  cited  here  will  be  given  in 
general  in  chronological  order,  to  indicate,  if  possible,  how  pres- 
ent views  have  actually  developed,  and  to  suggest  that  they 
may  at  any  time  require  modification  as  a  result  of  further 
research. 

Meischer  studied  the  formation  of  complex  from  simpler  phos- 
phorus compounds  in  the  adult  animal  body  by  observations 
upon  the  Rhine  salmon,  which  during  the  breeding  season  re- 
main a  long  time  in  fresh  water,  taking  no  food,  but  developing 
large  masses  of  roe  and  milt  at  the  expense  of  muscular  tissue. 
This  process  evidently  involves  the  formation  of  considerable 
amounts  of  nucleoproteins  and  phosphatids  from  simpler  pro- 
teins, fats,  and  phosphorus  compounds  of  the  muscles.  Paton  * 
has  studied  the  salmon  of  Scotland  with  similar  results.  Is  there 
then  any  advantage  in  feeding  phosphorus  in  organic  forms? 

Marcuse,t  followed  by  Steinitz,t  Zadik,§  and  Leipzlger,  || 
studied,  by  metabolism  experiments  on  dogs,  the  nutritive  value 
of  phosphoproteins,  when  fed  to  the  exclusion  of  phosphates 
and  when  contrasted  with  equivalent  amounts  of  phosphorus 
and  nitrogen  fed  in  the  form  of  mixtures  of  inorganic  phosphates 
and  simple  proteins.     Casein  and  ovovitellin  were  taken  as 

*  Journal  of  Physiology,  Vol.  22,  page  333- 

t  Archiv  fiir  die  gesammte  Physiologic  (Pfluger),  Vol.  67,  page  373- 

X  Ibid.,  Vol.  72,  page  75-  §  ^bid.,  Vol.  77.  page  i. 

II  Ibid.,  Vol.  78,  page  402. 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      247 

typical  phosphoproteins  and  compared  with  either  myosin  or 
edestin  fed  with  inorganic  phosphates.  Rohmann  *  summarized 
the  results  as  a  whole  and  found  a  striking  difference  in  the  phos- 
phorus balances  in  favor  of  the  phosphoproteins  as  against  the 
mixtures  of  simple  proteins  with  inorganic  phosphates.  The 
storage  of  nitrogen  was  also  more  pronounced  in  the  periods  in 
which  the  phosphorized  proteins  were  fed.  The  results  appear 
to  justify  Rohmann's  conclusion  that  the  nutritive  values  of 
phosphorized  and  phosphorus-free  proteins  are  not  entirely  the 
same,  the  former  being  especially  adapted  to  furnish  the  material 
for  tissue  growth. 

In  experiments  upon  men,  Ehrstrom  f  and  Gumpert  %  have 
found  that  a  smaller  amount  of  phosphorus  will  maintain  phos- 
phorus equilibrium  when  taken  in  the  form  of  casein  than  when 
taken  largely  as  dicalcium  phosphate  or  as  meat,  the  phosphorus 
of  which  is  largely  in  the  form  of  potassium  phosphate.  On  the 
other  hand  Keller  §  in  a  study  of  the  phosphorus  metabolism  of 
young  children  found  evidence  that  storage  of  phosphorus  was 
favored  by  food  (like  milk)  which  contained  a  liberal  supply  of 
phosphates  in  addition  to  the  organic  phosphorus  compounds; 
and  Von  Wendt  found  that  the  loss  of  phosphorus  occurring  on 
a  diet  very  poor  in  ash  could  be  greatly  reduced  by  the  addition 
of  dicalcium  phosphate  to  the  food. 

In  cow's  milk  the  greater  part  of  the  phosphorus  appears  to 
exist  as  phosphate,  but  there  can  be  no  doubt  that  the  milk 
phosphorus  as  a  whole  is  available  for  the  needs  of  the  young 
of  the  species,  especially  in  view  of  the  parallehsm  pointed  out 
by  Bunge  and  Abderhalden  between  the  phosphorus  and  cal- 
cium content  of  milk  and  the  rate  of  growth  of  the  young.  (See 
accompanying  table.) 

*  Berlin  klinische  Wochenschrift,  Vol.  35,  page  789. 

t  Skandinavisches  Archiv  jiir  Physiologic,  Vol.  14,  page  82. 

t  Medische  Klinik,  Vol.  i,  page  1037. 

§  Archiv  fur  Kinderheilkunde,  Vol.  29,  page  i. 


248 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


No.  OF  Days 

Required  to 

Double  the 

Birth  Weight 

Percentage  Composition  of  Milk  (Partial) 

Species 

Protein 

Ash 

Calcium 

Phosphorus 

Human 

Horse 

Cow 

Goat 

Sheep 

Swine 

Dog 

Rabbit 

180 
60 

47 
22 

15 

14 

9 

6 

1.6 
2.0 
3-5 
^■7 
4.9 
5.2 
7.4 
14.4 

0.2 

0.4 

0.7 

0.78 

0.84 

0.80 

1.33 
2.50 

0.02 
0.09 
0,12 
0.14 
0.18 
o.i8 
0.32 
0.65 

0.02 
0.06 
0.09 
0.18 
O.II 

0.14 

0.22 

0.43 

It  is,  however,  not  without  possible  significance  that  the  phos- 
phorus of  human  milk  is  mainly  in  organic  forms  (Soldner)  and 
that,  notwithstanding  its  much  lower  content  of  total  phos- 
phorus, human  milk  contains  as  high  a  percentage  of  lecithin 
as  does  cow's  milk  (Stoklasa).  An  infant  fed  on  diluted  cow's 
milk  must  therefore  receive  less  lecithin  than  the  breast-fed 
infant  while  it  may  receive  more  total  phosphorus. 

In  general  the  more  recent  investigations  favor  the  view  that 
the  body  can  use  inorganic  phosphates  to  meet  all  its  phosphorus 
requirements. 

Hart,  McCollum,  and  Fuller  showed  in  1909  that  with  young 
pigs  on  a  ration  too  poor  in  phosphorus  to  support  normal  growth 
the  deficit  could  be  made  good  by  feeding  phosphates  as  well  as 
by  feeding  foods  containing  organic  phosphorus  compounds. 

The  following  year  (1910)  McCollum  reported  that,  other 
things  being  satisfactory,  all  the  phosphorus  requirements  of  an 
animal  can  be  met  by  feeding  inorganic  phosphates.  In  one  of 
these  experiments  McCollum  kept  a  rat  for  104  days  on  diets 
of  purified  food  materials  in  which  phosphorus  was  given  only 
as  phosphate.  It  maintained  good  condition  but  suffered  some 
loss  of  weight  as  it  would  not  eat  enough  of  the  artificial  food 
to  meet  the  energy  requirement.  In  another  case  in  which  an 
amino  acid  mixture  from  the  hydrolysis  of  beef  muscle  was 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      249 

added  to  the  diet  the  food  was  eaten  more  readily  and  one  rat 
increased  in  weight  from  153  to  176  grams  while  receiving  only 
inorganic  phosphorus. 

As  young  rats  eat  unpalatable  food  more  readily  than  do 
adults,  McCoUum  fed  the  ration  containing  phosphate  as  sole 
source  of  phosphorus  to  young  growing  rats,  one  of  which  ate 
the  ration  for  127  days,  during  which  time  he  doubled  in  weight. 
At  the  end  of  this  experiment  the  rat  was  killed  and  analyzed 
and  found  to  be  of  normal  composition.  There  was  therefore 
no  reason  to  doubt  that  the  rat  synthesized  the  nucleoproteins 
and  phosphatids  of  his  growing  tissues  from  the  inorganic  phos- 
phorus of  his  food. 

Subsequent  experiments  by  McCoUum  and  Davis,  as  well  as 
those  of  Osborne  and  Mendel  described  in  connection  with  the 
discussion  of  proteins  (Chapter  III),  afford  many  instances  of 
long-continued  growth  of  rats  on  rations  made  up  of  "  isolated  " 
foodstuffs  in  which  all  or  nearly  all  of  the  phosphorus  was  in 
the  form  of  simple  phosphates. 

In  order  to  determine  whether  the  synthesis  of  lecithin  in  the 
animal  body  can  be  demonstrated  experimentally,  McCollum, 
Halpin,  and  Drescher  (191 2)  fed  3  hens  for  10  weeks  a  ration 
consisting  of  30  per  cent  skim  milk  powder  and  70  per  cent 
polished  rice,  both  of  which  were  freed  from  phosphatids.  This 
diet  it  will  be  noted  contained  phosphoprotein  as  well  as  phos- 
phate, but  very  Httle  fat,  and  it  was  beheved  no  phosphatid. 
The  hens  produced  eggs  in  normal  number  and  of  normal  com- 
position. The  phosphatid  in  the  eggs  produced  was  27.65  grams 
per  hen,  and  this  was  beheved  to  have  been  synthesized  rather 
than  to  have  come  from  material  previously  stored. 

FingerHng  (191 2)  kept  ducks  for  8  months  on  a  diet  of  pota- 
toes, blood  albumin,  starch,  and  lime  salts.  The  ducks  laid 
normally  and  the  phosphatid  content  of  the  eggs  produced  was 
determined.  Since  the  phosphatid  content  of  the  food  must 
have  been  small  and  the  feces  always  contained  some  lecithin- 


250  CHEMISTRY  OF  FOOD  AND   NUTRITION 

like  substances,  and  since  the  ducks  did  not  lose  weight,  Finger- 
ling  concludes  that  the  organic  phosphorus  compounds  in  the  eggs 
were  synthesized  from  inorganic  phosphorus  obtained  in  the  food. 

Later  he  fed  the  same  ducks  on  food  richer  in  organic  phos- 
phorus ;  and  as  they  produced  about  the  same  number  of  eggs 
of  similar  phosphatid  content  he  concluded  that  the  egg-phos- 
phatids  were  synthesized  as  readily  from  inorganic  as  from 
organic  phosphorus  compounds. 

The  evidence  seems  sufficient  to  warrant  the  statement  that 
animal  organisms  are  able  to  synthesize  nucleoproteins,  phospho- 
proteins,  and  phosphatids  from  inorganic  phosphate.  It  may, 
however,  still  be  questioned  whether  the  nutritive  conditions 
are  as  favorable  when  the  body  is  forced  to  do  this  as  when  a 
part  at  least  of  the  phosphorus  requirement  is  met  by  feeding 
phosphoproteins  and  phosphatids. 

The  above-mentioned  experiments  of  Rohmann  and  his 
pupils  on  dogs  and  of  Ehrstrom  and  Gumpert  on  men  seemed 
to  demonstrate  that  the  phosphoproteins  have  a  higher  food 
value  than  a  corresponding  mixture  of  simple  proteins  and  simple 
phosphates ;  and  the  recent  feeding  experiments,  while  showing 
the  efficiency  of  phosphates  in  meeting  the  phosphorus  require- 
ment, do  not  show  conclusively  that  the  phosphates  are  of  fully 
equal  value  with  the  organic  phosphorus  compounds.  Feeding 
experiments  of  long  duration  are  well  fitted  to  give  convincing 
evidence  on  the  former  point,  but  are  not  so  well  suited  for  the 
purposes  of  exact  quantitative  comparisons  because  the  very 
fact  of  their  long  duration  gives  opportunity  for  other  factors  to 
enter,  such  as  differences  in  vitality  among  the  experimental 
animals.  Masslow,  as  the  result  of  recent  investigation  of 
phosphorus  metabolism  during  growth,  holds  (1913)  that  for 
the  best  results  a  considerable  part  of  the  phosphorus  should 
preferably  be  supplied  in  organic  forms. 

Some  writers  have  argued  that  the  presence  in  extracts  of 
intestinal  mucosa  of  enzymes  capable  of  splitting  off  phosphoric 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      251 

acid  from  the  organic  phosphorus  compounds  of  the  food  may 
be  taken  as  evidence  that  phosphorus  is  absorbed  as  phosphoric 
acid  or  phosphate  whatever  the  form  in  which  it  occurs  in  the 
food ;  but  in  view  of  the  reversibihty  of  enzyme  action  and  the 
great  extent  to  which  it  is  influenced  by  conditions,  it  seems  pref- 
erable to  form  our  impressions  regarding  the  equivalence  or 
relative  values  of  the  different  phosphorus  compounds  from 
observations  or  experiments  upon  animals  rather  than  from 
tests  for  enzymes  in  tissue  extracts. 

Forbes  holds  that  even  though  the  phosphorus  be  absorbed 
as  inorganic  phosphate  there  is  advantage  in  having  it  supplied 
largely  in  organic  forms  since  "  much  larger  amounts  of  phos- 
phorus may  be  utilized  in  a  normal  manner  if  they  are  gradually 
liberated  in  the  usual  way  by  the  digestive  cleavage  of  the 
organic  complexes  with  which  they  are  combined."  * 

Forbes  and  Keith  (1914)  after  reviewing  most  thoroughly 
the  whole  literature  of  phosphorus  compounds  in  animal  metab- 
olism, draw,  among  others,  the  following  conclusion : 

"  That  organic  phosphorus  is  absolutely  essential  to  any 
animal  has  not  been  demonstrated.  The  proof  that  inorganic 
phosphorus  can  serve  all  of  the  purposes  for  which  any  animal 
needs  phosphorus  is  incomplete.!  There  is  much  evidence  to 
imply  that,  with  some  species  at  least,  some  organic  phosphorus 
compounds  are  more  useful  than  is  inorganic  phosphorus  in  the 
sense  of  being  more  readily  and  economically  utilized,  and  of 
maintaining  a  higher  state  of  vitality  as  revealed  by  tissue 
enzyme  estimations,  the  difference  probably  depending,  in  part 
at  least,  on  the  fact  of  the  partial  absorption  and  utilization  of 
organic  phosphorus  compounds  as  such,  wdthout  complete  diges- 
tive cleavage  "  (Ohio  Agricultural  Experiment  Station,  Tech- 
nical Bulletin  No.  5,  pages  364-365). 

*  Ohio  Agricultural  Experiment  Station,  Technical  Bulletin  No.  5,  page  357. 
t  (Some  of  the  experiments  of  Osborne  and  Mendel  and  of  McCollum  and  Davis 
have  appeared  since  the  above  was  written  by  Forbes  and  Keith.    H.  C.  S.) 


252  CHEMISTRY  OF  FOOD  AND  NUTRITION 

On  the  other  hand  Marshall  *  considers  the  evidence  fully 
suflScient  to  warrant  the  conclusion  that  organic  phosphorus 
compounds  are  of  no  more  value  as  food  than  are  the  inorganic 
phosphates. 

In  the  present  state  of  our  knowledge  there  is  at  least  no 
quantitative  measure  of  differences  in  nutritive  value  as  between 
different  forms  of  phosphorus.  If  differences  in  nutritive  value 
between  the  different  groups  of  phosphorus  compounds  exist, 
they  are  doubtless  in  favor  of  the  phosphoproteins  and  phos- 
phatids  and  are  more  significant  for  the  growing  than  for  the 
full-grown  organism.  For  the  reasons  explained  in  Chapters 
VIII,  XIII,  and  XIV  the  diet  of  growing  children  should 
always  contain  a  liberal  allowance  of  milk.  The  milk  will  pro- 
vide, in  addition  to  the  best  form  of  protein,  a  high  proportion 
of  phosphoprotein  and  also  significant  quantities  of  phosphatids. 
Hence  it  seems  justifiable  to  assume  that,  if  the  food  is  properly 
selected,  one  may  compute  its  total  phosphorus  content  and 
compare  it  with  the  total  phosphorus  requirement  of  the  body 
without  separate  computation  of  the  different  forms  of  phos- 
phorus. 

Estimation  of  the  Phosphorus  Requirement 

Since  phosphorus  compounds  are  essential  to  all  the  tissues 
of  the  body,  the  growth  of  new  tissue  requires  a  storage  of 
phosphorus  along  with  that  of  protein,  but  aside  from  this  it  is 
evident  that  the  phosphorus  metabolism  presents  a  separate 
problem  from  the  metabolism  of  protein. 

The  phosphorus  of  the  tissues  exists  largely  in  the  form  of 
nucleoproteins  —  the  characteristic  substances  of  cell  nuclei 
—  and,  as  these  are  important  in  metabolism,  there  was  a 
tendency  for  a  number  of  years  to  regard  the  phosphorus  elim- 
ination as  largely  a  measure  of  the  metabolism  of  nucleo- 
proteins somewhat  as  the  nitrogen  is  taken  as  a  measure  of  the 
*  Journal  of  the  American  Medical  Association,  Vol.  64,  page  573  (1915). 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      253 

metabolism  of  proteins  in  general.  It  is  probable,  however, 
that  such  a  view  of  the  phosphorus  metabolism  is  of  only  very 
limited  application,  because  of  the  influence  of  other  factors. 
Voit  showed  that  the  material  metaboHzed  in  fasting  comes 
largely  from  the  bones.  Undoubtedly  the  bones  take  part  in 
the  daily  metabolism,  and  while  they  may  undergo  a  less  active 
exchange  of  material  than  the  soft  tissues,  they  possess  such  a 
large  proportion  of  the  phosphorus  in  the  body  that  they  prob- 
ably contribute  a  considerable  part  of  what  is  metaboUzed  from 
day  to  day.  Moreover,  recent  investigations  upon  the  func- 
tion of  the  soluble  phosphates  of  the  blood  in  maintaining  neu- 
traHty  in  the  body  indicate  that  the  neutrahzation  of  acid  by 
conversion  of  di-  into  mono-phosphates  may  be  followed  by  an 
increased  excretion  of  the  acid  phosphate  in  the  urine.  Finally, 
it  is  evident  that  the  amount  of  phosphorus  metaboHzed  is 
very  directly  influenced  by  the  amount  taken  in  the  food. 

The  phosphorus  which  has  been  metaboHzed  is  excreted  from 
the  body  almost  entirely  in  the  form  of  inorganic  phosphates, 
the  organic  phosphorus  of  the  urine  constituting  as  a  rule  only 
I  to  3  per  cent  of  the  total.*  Carnivorous  animals  excrete  phos- 
phates mainly  through  the  kidneys,  but  in  the  herbivora  the 
excretion  occurs  almost  entirely  through  the  intestinal  wall, 
whether  the  phosphate  be  taken  by  the  mouth,  or  injected  sub- 
cutaneously,  or  be  formed  by  metabolism  of  organic  phosphorus 
compounds  in  the  body.  In  man,  the  eHmination  of  metab- 
oHzed phosphorus  is  partly  through  the  kidneys  and  partly 
through  the  intestinal  wall,  the  relative  quantities  in  urine  and 
feces  varying  within  rather  wide  limits.  As  a  rule,  foods  rich 
in  calcium,  or  which  yield  an  alkaline  ash,  tend  to  increase  the 
proportion  of  phosphorus  excreted  by  way  of  the  intestine. 

Attempts  have  sometimes  been  made  to  estimate  the  phos- 
phorus requirement  from  the  amount  excreted  in  the  urine. 

*  Some  investigators  have  doubted  the  occurrence  of  organic  phosphorus  in  urine 
while  others  have  estimated  it  as  high  as  6  per  cent  of  the  total  urinary  phosphorus. 


254 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


The  results  thus  obtained  are  always  too  low  (usually  very  much 
so),  and  are  largely  responsible  for  the  fact  that  the  amount  of 
phosphorus  required  for  the  normal  nutrition  of  man  is  seriously 
underestimated  in  many  of  the  standard  textbooks. 

Since  the  excretion  of  metaboKzed  phosphorus  through  the 
intestine  is  in  man  too  large  to  be  neglected  and  too  variable  to 
be  allowed  for  by  calculation,  we  can  expect  reliable  data  on 
phosphorus  requirements  from  those  experiments  only  in  which 
the  amounts  of  phosphorus  are  actually  determined  in  food,  in 
feces,  and  in  urine.  In  such  experiments  it  is  found  (as  in  the 
case  of  nitrogen)  that  the  output  obtained  upon  the  experi- 
mental days  is  influenced  not  only  by  the  food  taken  at  the 
time,  but  also  by  the  rate  of  metaboHsm  to  which  the  body  had 
been  accustomed  on  the  preceding  days.  This  is  shown  by  the 
following  results  obtained  in  a  12-day  series  of  experiments 
upon  a  healthy  man: 


Phosphorus  Metabolism  with  Different  Amounts  of  Phosphorus 

IN  the  Food 


Experimental  Period 

Phosphorus  per  Day 

No. 

Duration 

In  Food 
Grams 

In  Feces 
Grams 

In  Urine 
Grams 

Output 
Grams 

Balance 
Grams 

I 

II 

III 

3  days 
6  days 
3  days 

0.40 
0.77 
1.51 

045 
0.19 
0.50 

0.70 
0.72 
0.99 

1. 15 
0.91 
1.49 

-0.75 
—  0.14 
+  0.02 

Here  the  output  of  phosphorus  was  greater  in  the  first  period 
with  0.40  gram  in  the  food  than  in  the  second  when  the  food 
furnished  0.77  gram,  probably  because  the  first  period  followed 
and  was  influenced  by  a  preceding  diet  fairly  rich  in  phosphorus, 
whereas  the  output  in  Period  II  was  influenced  by  the  low- 
phosphorus  diet  of  Period  I.  For  the  same  reason  Period  II 
offered  favorable  conditions  for  the  estabUshment  of  equihbrium 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      255 

on  a  minimum  diet,  and  the  results  show  that  in  this  case  the 
subject  was  unable  to  reach  equilibrium  on  0.77  gram  per  day, 
the  output  averaging  0.91  gram.  When  the  intake  was  in- 
creased to  1. 5 1  grams,  the  output  rose  rapidly  and  averaged 
1.49  grams.  In  this  case  the  amount  which  would  have  been 
just  sufficient  for  equilibrium  evidently  lay  between  0.91  and 
1.49  grams  per  day.  By  means  of  well-planned  experiments  or 
series  of  experiments  it  is  possible  to  fix  for  a  given  individual 
much  narrower  limits  within  which  the  exact  amount  required 
for  equilibrium  must  he,  and  when  it  is  known  that  the  intake 
approximates  this  required  amount,  it  is  justifiable  to  regard 
the  output  as  an  indication  of  the  normal  nutritive  requirement. 
Study  of  the  data  of  93  such  phosphorus  balance  experiments 
upon  27  subjects,  21  men  and  6  women,  has  shown  a  range  of 
0.52  to  1.75  grams  with  an  average  of  0.96  gram  phosphorus 
(2.20  grams  P2O6)  per  70  kilograms  of  body  weight  per  day. 
This  corresponds  with  the  average  requirement  of  50  grams 
protein  per  day  per  man  of  70  kilograms  as  estimated  on  page 
220.  Allowing  50  per  cent  above  the  bare  minimum  would  give 
a  phosphorus  "  standard  "  of  1.44  grams  (3.30  grams  P2O5) 
corresponding  to  a  protein  "  standard  "  of  75  grams. 

Phosphorus  in  Food  Materials  and  Typical  Dietaries 

A  comparison  of  the  amounts  of  phosphorus  contained  in  the 
food  of  typical  American  famiUes  with  the  amounts  metaboHzed 
in  the  experiments  above  mentioned  indicates  that  a  freely 
chosen  diet  does  not  always  furnish  an  abundance  of  phosphorus 
compounds.  In  150  American  dietaries  of  families  or  larger 
groups  believed  to  be  fairly  representative,  the  estimated  amount 
of  phosphorus  furnished  per  man  per  day  was  below  0.96  gram 
in  7  cases,  while  in  no  case  was  there  less  than  50  grams  of  pro- 
tein per  man  per  day.  If  we  allow  a  margin  of  50  per  cent  for 
safety  in  both  protein  and  phosphorus,  we  find  8  per  cent  of  the 
dietaries  below  the  protein  standard  of  75  grams  and  41  per 


256  CHEMISTRY  OF   FOOD    AND  NUTRITION 

Approximate  Amounts  of  Phosphorus  in  Food  Materials 


Food 

Phosphorus 

PER  100  Grams 

Edible  Substance 

Phosphorus 

PER  100  Grams 

Protein 

Phosphorus 
PER  3000 
Calories 

Beef,  all  lean 

Eggs       

Egg  yolk     ....... 

Milk 

Cheese 

Wheat,  entire  grain  .     .     . 
White  flour 

Rice,  polished      .... 

Oatmeal 

Beans,  dried 

Beets 

Carrots 

Potatoes 

Turnips , 

Apples 

Bananas      .     .     .     .     .     . 

Oranges 

Prunes,  dried 

Almonds 

Peanuts       ...... 

Walnuts 

0.218 

.180 
•524 

.093 
.683 

•423 
.092 

.096 

.392 

.471 
•039 
.046 
.058 
.046 

.012 
.031 
.021 
.105 

.465 
.399 

•357 

0.96 

1.35 
2.73 

2.82 
2.58 

3.25 
.81 

1. 19 

2.36 

2.20 
2.42 
4.17 
2.60 
3.55 

3.15 
2.35 
2.58 
S.oo 

2.25 

I-S5 
1.96 

5-2 

3.66 
3-54 

4.02 
4.68 

3.54 
.78 

.81 

2.97 

4.11 
2.52 
3.03 
2.07 

3.51 

0.60 

0-93 
1.20 

1-05 

2.16 
2.19 
1-53 

cent  below  the  phosphorus  standard  of  1.44  grams.  These 
results  indicate  plainly  that  present  food  habits  are  more  likely 
to  lead  to  a  deficiency  of  phosphorus  compounds  than  to  a 
deficiency  of  protein  in  the  diet,  and  it  is  not  improbable  that 
many  cases  of  malnutrition  are  really  due  to  an  inadequate 
supply  of  phosphorus  compounds. 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      257 

That  the  cases  of  low  phosphorus  dietaries  are  not  to  be 
ascribed  simply  to  inadequacy  of  the  total  food  supply  of  these 
famihes  was  shown  by  computing  the  amounts  of  phosphorus 
which  would  have  been  furnished  in  each  case  had  the  total 
amount  of  food  been  so  increased  or  decreased  as  to  furnish 
just  3000  Calories  per  man  per  day.  On  this  basis  only  one 
of  the  1 50  dietaries  shows  less  than  0.96  gram,  but  49  of  them  or 
33  per  cent  show  less  than  i  ,44  grams  of  phosphorus,  as  against 
only  2  per  cent  with  less  than  75  grams  of  protein,  per  3000 
Calories. 

The  table  on  the  preceding  page  compares  some  staple  foods 
as  sources  of  phosphorus. 

It  will  be  seen  that,  whether  compared  on  the  basis  of  weight, 
or  of  protein  content  or  energy  value,  the  different  staple  foods 
vary  greatly  in  phosphorus  content.  In  the  planning  of  dietaries 
this  fact  should  be  kept  in  mind  and  care  taken  that  foods 
fairly  rich  in  phosphorus  be  adequately  represented  in  each  day's 
food. 

REFERENCES 

(See  also  the  references  at  the  end  of  the  next  chapter.) 

Abderhalden.    Lehrbuch  der  Physiologische  Chemie,  3  Aufl.,  Vorlesungen. 

34-37. 
Anderson.     The  Organic  Phosphoric  Acid  Compound  of  Wheat  Bran, 

Journal  of  Biological  Chemistry,  Vol.  20,  pages  463,  475,  483,  493  (1915), 
Babcock.    Metabolic  Water.    Wisconsin  Agricultural  Experiment  Station, 

Research  Bulletin  22  (191 2). 
Bayliss.    Principles  of  General  Physiology,  Chapters  7  and  8. 
Benedict.    A    Study    of    Prolonged    Fasting.    Carnegie    Institution    of 

Washington,  Publication  No.  203,  pages  247-291. 
Boutwell.    The  Phytic  Acid  of  the  Wheat  Kernel  and  Some  of  Its  Salts. 

Journal  of  the  American  Chemical  Society,  Vol.  39,  page  491  (191 7). 
BuNGE.     Physiological  and  Pathological  Chemistry,  Chapters  7  and  8. 
Ehrstrom.     Phosphorus    MetaboHsm    in    Adult    Man.     Skandinavisches 

Archivfiir  Physiologic,  Vol.  14,  pages  82-111  (1903). 
Emmett  and  Grtndley.    a  Study  of  the  Phosphorus  Content  of  Flesh. 

Journal  of  the  American  Chemical  Society,  Vol.  28,  pages  25-63  (1906). 
s 


25B  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Eppler.  Investigations  of  Phosphatids,  especially  those  of  the  Egg  Yolk. 
Zeitschrift  fur  physiologische  Chemie,  Vol.  87,  pages  233-254  (1913). 

FiNGERLiNG.  Formation  of  Organic  from  Inorganic  Phosphorus  Compounds 
in  the  Animal  Body.  Zeitschrift  fur  Biologie,  Vol.  38,  page  448 ;  Vol. 
39,  page  239  (191 2). 

Forbes.  The  Mineral  Elements  in  Animal  Nutrition,  Ohio  Agricultural 
Experiment  Station,  Bulletin  201  (1909). 

Forbes.  Specific  Effects  of  Rations  upon  the  Development  of  Swine. 
Ohio  Agricultural  Experiment  Station,  Bulletins  213  and  283. 

Forbes  and  Keith.  A  Review  of  the  Literature  of  Phosphorus  Compounds 
in  Animal  Metabolism.  Ohio  Agriculture  Experiment  Station; 
Technical  Bulletin  No.  5  (1914). 

Hart,  McCollum,  and  Humphrey.  R6le  of  the  Ash  Constituents  of  Wheat 
Bran  in  the  Metabolism  of  Herbivora.  American  Journal  of  Physiol- 
ogy, Vol.  24,  pages  86-103  (1910). 

Hawk.  The  Relation  of  Water  to  Certain  Life  Processes  and  more  es- 
pecially to  Nutrition.     Biochemical  Bulletin,  Vol.  3,  page  420  (1914). 

GuMPERT.  Metabolism  of  Nitrogen,  Phosphorus,  Calcium,  and  Magnesium 
in  Man.    Medizinische  Klinik,  Vol.  i,  page  1037  (1905). 

Hart,  McCollum,  and  Fuller.  The  R6le  of  Inorganic  Phosphorus  in 
the  Nutrition  of  Animals.  Wisconsin  Agricultural  Experiment  Station, 
Research  Bulletin  No.  i ;  American  Journal  of  Physiology,  Vol.  2t„ 
page  246  (1908-1909). 

Herbst.  Calcium  and  Phosphorus  in  Growth  at  the  End  of  Childhood. 
Zeitschrift  der  Kinder heilkunde.  Vol.  7,  page  i6i  (1913). 

Jordan,  Hart,  and  Patten.  Metabolism  and  Physiological  Effects  of 
Phosphorus  Compounds  of  Wheat  Bran.  New  York  State  Agricultural 
Experiment  Station,  Technical  Bulletin  No.  i ;  and  American  Journal 
of  Physiology,  Vol.  16,  page  268  (1906). 

McCollum.  Nuclein  Synthesis  in  the  Animal  Body.  Wisconsin  Agri- 
cultural Experiment  Station,  Research  Bulletin  No.  8  (1910). 

McCollum,  Halpin,  and  Drescher.  Synthesis  of  Lecithin  in  the  Hen 
and  the  Character  of  the  Lecithin  Produced.  Journal  of  Biological 
Chemistry,  Vol.  13,  page  219  (191 2). 

McCrudden  and  Fales.  Complete  Balance  Studies  of  Nitrogen,  Sulphur, 
Phosphorus,  Calcium  and  Magnesium  in  Intestinal  InfantiHsm.  Jour- 
nal  of  Experimental  Medicine,  Vol.  15,  page  450  (191 2). 

McLean,  On  the  Occurrence  of  a  Mon-amino-diphosphatid  Lecithin-like 
Body  in  Egg  Yolk.     Biochemical  Journal,  Vol.  4,  page  168  (1909). 

Marshall.  Comparison  of  Value  of  Organic  and  Inorganic  Phosphorus. 
Journal  of  the  American  Medical  Association,  Vol.  64,  page  573  (1915). 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      259 

Masslow.  Significance  of  Phosphorus  for  the  Growing  Organism.  Bio- 
chemisches  Zeitschrift,  Vol.  55,  page  45 ;  Vol.  56,  page  174  (1913). 

Meischer.  Biochemical  Studies  on  the  Rhine  Salmon.  Archiv  fiir  Ex- 
perimental Pathologie  und  Pharmacologie,  Vol.  37,  page  100  (1896). 

Plimmer.  The  Metabolism  of  Organic  Phosphorus  Compounds.  Their 
Hydrolysis  by  the  Action  of  Enzymes.  Biochemical  Journal,  Vol.  7, 
page  48  (1913)- 

Schlossmann.  On  the  Kind  and  Amount  of  Phosphorus  in  Milk  and  its 
Significance  in  Infant  Nutrition.  Archiv  fiir  Kinderheilkimde,  Vol.  40, 
page  I  (1905). 

Sherman,  Mettler,  and  Sinclair.  Calcium,  Magnesium,  and  Phos- 
phorus in  Food  and  Nutrition.  U.  S.  Department  of  Agriculture, 
Ofiice  of  Experiment  Stations,  Bulletin  227  (1910). 


CHAPTER  X 

INORGANIC   FOODSTUFFS   AND   THE   MINERAL 
METABOLISM    (Continued) 

Metabolism  of  Sodium,  Potassium,  Calcium,  Magnesium 

The  distribution  of  sodium  and  potassium  in  the  body  and 
some  of  their  mutual  relations  in  metabolism  have  been  referred 
to  in  the  section  on  the  chlorides.  The  distribution  and  func- 
tions of  calcium  have  been  studied  in  greater  detail  than  those 
of  magnesium.  It  is  estimated  that  about  85  per  cent  of  the 
mineral  matter  of  bone,  or  at  least  three  fourths  of  the  entire 
ash  of  the  body,  consists  of  calcium  phosphate.  Probably  over 
99  per  cent  of  the  calcium  in  the  body  belongs  to  the  bones,  the 
remainder  occurring  as  an  essential  constituent  of  the  soft  tissues 
and  body  fluids.  Of  the  magnesium  in  the  body  about  71  per 
cent  is  contained  in  the  bones  (Lusk).  The  muscles  contain 
considerably  more  magnesium  than  calcium ;  the  blood  contains 
more  calcium  than  magnesium. 

That  calcium  salts  are  necessary  to  the  coagulation  of  the 
blood  has  long  been  known  and  frequently  cited  as  an  example 
of  the  great  importance  of  calcium  salts  to  the  animal  economy. 
Equally  striking  is  the  function  of  these  salts  in  regulating  the 
action  of  heart  muscle. 

It  is  well  known  that  heart  muscle  may  be  kept  beating  nor- 
mally for  hours  after  removal  from  the  body  when  supplied, 
under  proper  conditions,  with  an  artificial  circulation  of  blood 
or  lymph  or  a  water  solution  of  blood  ash.  Howell,  Loeb,  and 
others  have  studied  the  parts  played  by  the  several  ash  con- 

260 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      261 

stituents.  The  sodium  salts  take  the  chief  part  in  the  main- 
tenance of  normal  osmotic  pressure  and  have  also  a  specific 
influence.  Contractility  and  irritabiHty  disappear  if  they  are 
absent,  but  when  present  alone  they  produce  relaxation  of  the 
muscle  tissue.  Calcium  salts  also,  although  occurring  in  blood 
in  very  much  smaller  quantity,  are  absolutely  necessary  to  the 
normal  action  of  the  heart  muscle ;  while  if  present  in  quantities 
above  normal,  they  cause  a  condition  of  tonic  contraction  ("  cal- 
cium rigor  ")•  There  is  a  balance  which  must  be  maintained 
between  calcium  on  the  one  hand  and  sodium  (and  potassium) 
on  the  other.  Thus  it  is  found  that  the  alternate  contractions 
and  relaxations  which  constitute  the  normal  beating  of  the  heart 
are  dependent  in  part  upon  the  presence  of  a  sufficient  but  not 
excessive  concentration  of  calcium  salts,  and  in  part  upon  the 
quantitative  relationship  of  calcium  to  sodium  and  potassium, 
in  the  fluid  which  bathes  the  heart  muscle.  Other  active  tissues 
of  the  body  doubtless  have  analogous  requirements  as  to  in- 
organic salts. 

Regarding  the  adequacy  of  the  ordinary  intake  to  meet  the 
specific  requirements  for  sodium,  potassium,  calcium,  and  mag- 
nesium, it  would  seem  that  only  in  the  case  of  calcium  is  it  ordi- 
narily necessary  to  take  thought  in  the  selection  of  food  materials 
or  the  arrangement  of  dietaries.  The  amount  of  sodium  chlo- 
ride usually  added  to  food  is  much  more  than  sufficient  to  meet 
the  sodium  requirement  of  the  body,  even  if  the  natural  sodium 
content  of  the  food  be  entirely  disregarded.  Potassium  and 
magnesium  are  relatively  abundant  in  meat  (muscle)  and  also 
in  most  plant  tissues,  so  that  an  ordinary  mixed  diet,  unless  it 
consist  too  largely  of  highly  refined  food  materials,  will  usually 
furnish  a  safe  surplus  of  these  elements.  Dietaries  entirely 
adequate  in  energy  value  and  protein  content  may,  however, 
contain  too  little  calcium.  Calcium  requirement  is  therefore 
a  question  of  much  practical  importance  in  human  nutrition, 
and  requires  quantitative  study. 


262  CHEMISTRY  OF   FOOD  AND   NUTRITION 

The  Calcium  Requirement 

Calcium  constitutes  a  larger  proportion  of  the  body  weight 
(about  2  per  cent)  than  does  any  other  of  the  "  inorganic  "  ele- 
ments. It  is  very  unevenly  distributed  in  the  body,  over  99  per 
cent  of  the  total  amount  being  in  the  bones.  It  is  also  very 
irregularly  distributed  among  the  staple  articles  of  food,  many 
of  which  are  extremely  poor  in  calcium,  while  milk  contains  it 
in  abundance.  The  "  ordinary  mixed  diet  "  of  Americans  and 
Europeans,  at  least  among  dwellers  in  cities  and  towns,  is  prob- 
ably more  often  deficient  in  calcium  than  in  any  other  chemi- 
cal element. 

In  studying  the  effects  of  insufficient  calcium,  Voit  kept  a 
pigeon  for  a  year  on  calcium-poor  food  without  observing  any 
effects  attributable  to  the  diet  until  the  bird  was  killed  and  dis- 
sected, when  it  appeared  that,  although  the  bones  concerned 
in  locomotion  were  still  sound,  there  was  a  marked  wasting  of 
calcium  salts  from  other  bones  such  as  the  skull  and  sternum, 
which  in  places  were  even  perforated.  Thus  in  adults  there 
may  be  a  continued  loss  of  calcium  without  the  appearance  of 
any  distinct  symptoms  because  the  losses  from  the  blood  and 
soft  tissues  may  be  replaced  by  calcium  withdrawn  from  the 
bones.  The  injurious  effect  of  an  insufficient  intake  of  calcium 
is  of  course  more  noticeable  with  growing  than  with  full-grown 
animals.  Abnormal  weakness  and  flexibihty  of  the  bones  (re- 
sembling the  condition  of  rickets  in  children)  has  been  produced 
experimentally  by  feeding  puppies  with  lean  and  fat  meat  only, 
while  others  of  the  same  litter,  receiving  the  same  food,  but  with 
the  addition  of  bones  to  gnaw,  developed  normally.  In  this  con- 
nection it  should  be  remembered  that  no  animal  is  literally  car- 
nivorous in  nature,  that  is,  none  lives  on  flesh  alone ;  the  animals 
called  carnivora  always  eat  more  or  less  of  the  bones  of  their  prey. 

According  to  Herter  *  many  cases  of  arrested  development  in 

*  On  Infantilism  from  Chronic  Intestinal  Infection,  New  York,  1908. 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      263 

infancy  may  be  due  to  an  insufficient  assimilation  of  calcium 
from  the  food.  Such  a  deficiency  in  the  amount  assimilated 
may  be  due  to  defective  digestion  or  to  a  diet  inadequate  in 
calcium  content. 

Many  medical  writers  have  attributed  different  diseases  to 
inadequate  calcium  supply  or  disturbance  of  calcium  metabo- 
lism. Conclusive  proof  or  disproof  of  such  theories  would  how- 
ever require  more  detailed  and  exact  quantitative  studies  of 
the  intake  and  output  of  calcium  in  health,  and  the  amounts  re- 
quired in  normal  nutrition  at  different  ages  and  under  different 
conditions,  than  have  yet  been  made. 

The  fact  that  normal  urine  has  a  low  calcium  content  while 
the  feces  usually  contain  much  the  greater  part  of  the  calcium 
which  has  been  taken  in  the  food  has  often  been  interpreted  as 
meaning  that  the  absorption  of  food  calcium  is  poor  or  that  the 
calcium  requirement  of  the  body  is  low.  It  is  now  known,  how- 
ever, from  experimental  evidence,  that  most  of  the  calcium 
which  has  been  absorbed  and  carried  through  the  metaboHc 
processes  is  normally  excreted  through  the  intestinal  wall  and 
thus  leaves  the  body  in  the  feces  instead  of  the  urine.  When 
the  diet  is  very  poor  in  calcium  and  the  output  of  this  element 
materially  exceeds  the  intake,  the  feces  often  contain  a  larger 
amount  of  calcium  than  was  present  in  the  food. 

Observations  upon  Breithaupt  and  Cetti  showed  a  consider- 
able elimination  of  calcium  in  the  feces  during  fasting.  On  the 
other  hand,  Benedict  reports  the  result  of  a  31-day  fast  during 
which  no  feces  were  passed,  but  considerable  quantities  of 
calcium  continued  to  be  lost  through  the  urine  throughout  the 
entire  period. 

On  account  of  the  fluctuating  distribution  of  the  calcium  be- 
tween urine  and  feces,  conclusions  regarding  the  calcium  re- 
quirement can  properly  be  drawn  only  from  those  experiments 
in  which  the  amounts  of  this  element  in  the  food,  in  the  feces,  and 
in  the  urine  have  been  directly  determined.    A  compilation  of 


264  CHEMISTRY  OF  FOOD  AND  NUTRITION 

such  experiments  has  been  made,  and  the  reported  results  cal- 
culated to  a  uniform  basis  of  70  kilograms  of  body  weight.  On 
this  basis,  63  experiments  on  10  subjects  (6  men  and  4  women) 
show  calcium  outputs  ranging  from  0.27  to  0.78  gram  and 
averaging  0.45  gram  of  calcium  "  per  man  per  day."  This 
includes  the  experiments  which  appear  most  reliable  as  indicat- 
ing the  actual  (minimum)  requirement  in  that  the  food  did  not 
furnish  an  excess  of  calcium  over  the  needs  of  the  subject,  and 
the  calcium  balance  showed  a  reasonable  approach  toward 
equilibrium.  It  will  be  noted  that  this  average  of  0.45  gram 
calcium  (equivalent  to  0.63  gram  CaO)  represents  the  expendi- 
ture under  conditions  of  closely  restricted  calcium  intake.  It 
corresponds  to  the  average  of  49.2  grams  of  protein  per  man  per 
day  reached  on  page  220,  and  approximates  the  minimum  of 
actual  need  rather  than  a  normal  allowance.  The  margin  for 
safety  should  probably  be  larger  for  calcium  than  for  protein 
because  of  the  likelihood  of  relatively  greater  losses  in  cooking 
and  in  digestion,  while  there  is  much  less  danger  of  any  injurious 
result  from  surplus  calcium  than  from  surplus  protein.  Nelson 
and  Williams  have  recently  found  the  calcium  output  of  four 
healthy  men  on  normal  unrestricted  diet  to  range  from  0.68  to 
1.02  grams  of  calcium  (0.95  to  1.43  grams  of  CaO)  per  day. 
Here  as  in  the  case  of  protein  the  rate  of  metabolism  to  be  ex- 
pected in  a  normal  man  on  unrestricted  diet  and  well  fed,  ac- 
cording to  American  standards,  runs  from  50  to  100  per  cent 
above  the  amount  which  would  probably  suffice  to  meet  the 
actual  requirement. 

The  calcium  requirements  of  women  are  greatly  increased 
by  maternity.  The  need  of  an  abundance  of  calcium  for  the 
rapidly  growing  skeleton  of  an  infant  is  obvious.  Before  birth, 
and  normally  for  several  months  after,  this  demand  of  the  child 
is  satisfied  through  the  mother,  whose  calcium  requirement  is 
thus  greatly  increased.  The  weakening  of  the  bones  and  teeth 
which  is  said  to  be  a  common  accompaniment  of  pregnancy  and 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      265 

lactation  is  held  by  Bunge  to  be  largely  due  to  a  withdrawal  of 
calcium  from  these  structures  to  meet  the  nutritive  require- 
ments of  the  embryo  or  the  nursling. 

Lusk  also  emphasizes  the  importance  of  a  diet  rich  in  calcium 
for  pregnant  women,  especially  during  the  last  ten  weeks  of 
pregnancy,  when  the  fetus  is  storing  calcium  at  a  rapid  rate. 
He  cites  *  the  data  of  Hoffstrom,f  who  computed  in  consider- 
able detail  the  demands  of  the  fetus  upon  the  mother  for  nitro- 
gen, phosphorus,  calcium,  and  magnesium  at  different  stages 
of  intrauterine  life. 

Strong  confirmation  of  this  has  recently  been  obtained  from 
investigation  of  farm  animals.  The  experiments  of  Steenbock 
and  Hart  show  that  the  production  of  milk  in  cows  and  goats 
causes  a  heavy  drain  upon  the  calcium  of  the  skeleton  unless 
the  amount  of  calcium  contained  in  the  food  be  very  abundant. 
They  also  point  out  that  the  mammary  glands  likewise  make 
large  demands  upon  the  phosphorus  supply  and  suggest  that 
if  the  food  be  not  rich  in  phosphorus  the  destruction  of  bone 
tissue  to  furnish  phosphorus  for  milk  production  may  result 
in  still  further  loss  of  calcium  from  the  body. 

Forbes  and  Beegle  in  studying  the  mineral  metabolism  of 
the  milch  cow  found  a  heavy  loss  of  body  calcium,  notwithstand- 
ing the  fact  that  the  food  was  beheved  to  supply  Hberal  amounts 
of  all  essential -elements  and  was  eaten  in  sufficient  quantity  to 
induce  storage  of  nitrogen.  That  calcium  may  be  lost  from  the 
body  while  nitrogen  is  being  stored  has  also  been  emphasized  by 
several  other  investigators  (Steenbock  and  Hart,  Weiser,  and 
others) .  According  to  Forbes  it  may  be  necessary  to  continue  high 
calcium  feeding  for  some  time  after  the  cessation  of  lactation,  in 
order  to  replace  the  calcium  which  the  maternal  organism  has  lost. 

In  children  after  weaning  and  throughout  early  childhood  there 
are  apt  to  be  frequent  disturbances  of  the  absorption  and  metab- 

*  Lusk.    Science  of  Nutrition,  3d  edition,  pages  389-390. 

t  Hoffstrom.    Skandinavisches  Archiv  jUr  Physiologie,  Vol.  23,  page  326  (1910). 


266  CHEMISTRY  OF  FOOD  AND   NUTRITION 

olism  of  calcium,  in  some  cases  due  to  distinct  disorders  of 
digestion,  in  other  cases  to  more  obscure  irregularities  in  nutri- 
tion. In  order  that  these  fluctuations  shall  not  interfere  with 
the  steady  growth  of  the  child,  it  is  obvious  that  the  food  must 
furnish  a  fairly  Hberal  surplus  of  calcium.  Even  under  the 
most  favorable  conditions,,  a  rapidly  growing  child  will  pre- 
sumably need  more  bone-making  material  in  proportion  to  its 
total  food  than  do  adults,  who  alone  have  served  as  subjects  for 
the  metabolism  experiments  upon  which  our  present  estimate 
of  calcium  requirement  is  based.  Camerer,  in  summarizing 
a  long  series  of  investigations  upon  the  food  requirements  of 
children  at  different  ages,  concluded  that  the  amount  of  calcium 
received  by  the  average  nursling  is  just  about  sufficient  to  main- 
tain a  normal  rate  of  growth,  leaving  little  if  any  "  margin  of 
safety  "  ;  and  Bunge,  from  a  comparison  of  the  calcium  contents 
of  different  staple  foods,  points  out  that  calcium  more  than  any 
other  inorganic  element  is  likely  to  be  deficient  as  the  result  of 
the  change  of  diet  from  mother's  milk  to  other  forms  of  food. 

Herter  *  estimates  that  in  order  to  support  normal  growth 
of  the  skeleton  there  must  be  an  average  storage  of  about  37 
grams  of  calcium  (51.6  grams  of  calcium  oxide)  annually  through- 
out the  period  from  the  third  to  the  sixteenth  year.  This  means 
an  average  daily  storage  of  somewhat  more  than  o.io  gram  of 
calcium  during  this  thirteen-year  period.  In  order  to  accom- 
plish such  a  storage  it  is  plain  that  the  daily  food  of  the  child 
must  contain  a  surplus  of  more  than  o.io  gram  of  calcium  per 
day  beyond  the  amount  required  for  maintenance,  which  latter 
amount  should  provide  for  the  frequent  failures  of  complete 
utilization  which  have  already  been  mentioned. 

Herbst  f  studied  the  calcium  metabolism  of  6  boys  between 
the  ages  of  6  and  14  years  and  found  that  they  were  storing  from 
0.010  to  0.016  gram  of  calcium  per  kilogram  per  day,  or  0.21 

*  Infantilism. 

t  Jahrh.  Kinderheilkunde,  Vol.  76.    Ergdnzungshejt,  pages  40-130. 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      267 

to  0.39  gram  per  capita  per  day.  If  normal  growth  of  boys  of 
these  ages  involves  such  a  large  storage  of  calcium,  it  is  plain 
that  the  food  of  such  boys  must  be  rich  in  calcium  if  they  are 
to  develop  advantageously.  These  boys  consumed  about  3  to  4 
times  as  much  calcium  in  proportion  to  their  weight  as  is  required 
for  the  maintenance  of  men. 

From  such  considerations  as  these  it  is  evident  that  one  should 
be  very  Hberal  in  calculating  the  amount  of  calcium  to  be  sup- 
pHed  to  growing  children. 

If  0.45  gram  is  the  minimum  on  which  an  average  man  can 
maintain  equilibrium,  it  would  seem  that  the  food  of  a  family 
should  furnish  at  least  0.67  gram  *  of  calcium  or  0.9  to  i.o  gram 
of  calcium  oxide  per  man  per  day.  This  is  less  than  is  advo- 
cated by  such  recent  writers  as  Albu  and  Neuberg,  Gautier, 
Obendoerffer,  and  Emmerich  and  Loew,  or  reported  by  Nelson 
and  WilUams ;  yet  about  50  per  cent  of  the  American  dietaries 
which  have  so  far  been  studied  with  respect  to  their  ash  con- 
stituents show  less  than  0.67  gram  of  calcium  per  man  per  day, 
and  about  15  per  cent  of  them  show  less  than  0.45  gram  calcium 
(0.63  gram  CaO)  per  man  per  day.  In  some  cases  the  deficiency 
in  calcium  is  incidental  to  a  general  deficiency  in  the  amount 
of  food ;  but  if  the  food  consumed  in  each  dietary  had  been  in- 
creased or  decreased  to  just  3000  Calories  there  would  have  been 
less  than  0.67  gram  of  calcium  in  46  per  cent,  and  less  than  0.45 
gram  in  8  per  cent  of  the  cases.  Since  inorganic  forms  of  cal- 
cium are  utihzed  in  nutrition,  the  lime  of  the  drinking  water 
may  be  added  to  that  of  the  food  in  calculating  the  amount 
consumed,  and  to  this  extent  the  actual  nutritive  supply  may 
be  greater  than  the  dietary  studies  show,  but  unless  a  very 
"  hard  "  water  be  used  for  drinking,  it  is  unHkely  that  the  Hme 
from  this  source  will  cover  more  than  a  small  part  of  the  cal- 
cium requirement.     It  is  probable  too  that  losses  of  food  cal- 

*  This  amounts  to  setting  a  tentative  "standard  "  50  per  cent  higher  than  the 
average  minimum,  as  in  the  cases  of  protein  and  of  phosphorus. 


268  CHEMISTRY  OF  FOOD  AND  NUTRITION 

cium  in  cooking  may  fully  offset  the  calcium  obtained  from  the 
drinking  water.  Apparently  the  American  dietary  is  more 
often  deficient  in  calcium  than  in  any  other  element ;  certainly 
more  attention  should  be  paid  to  the  choice  of  such  foods  as  will 
increase  the  calcium  content  of  the  dietary.  The  use  of  more 
milk  and  vegetables  with  less  meat  and  sugar  will  accomplish 
this  and  usually  improve  the  diet  in  other  directions  as  well. 

Calcium  Content  of  Typical  Foods 

The  table  on  the  following  page  shows  the  comparative 
richness  in  calcium  of  a  number  of  staple  articles  of  food. 

It  will  be  seen  that  there  are  enormous  differences  in  the  cal- 
cium content  of  different  foods,  whether  expressed  in  percentage 
of  the  food  material  or  in  relation  to  its  protein  content  or 
energy  value.  Meat  is  exceedingly  poor  in  calcium  and  is 
therefore,  notwithstanding  its  high  protein  content,  a  very  one- 
sided and  inadequate  source  of  "  building  material."  Milk  is 
so  rich  in  calcium  that  one  need  take  only  400  Calories  of  milk 
to  obtain -the  entire  day's  supply  of  this  element,  while  to  get 
the  same  amount  of  calcium  from  round  steak  and  white  bread 
it  would  be  necessary  to  take  10,000  Calories.  Polished  rice 
and  new  process  corn  meal  are  even  poorer  in  calcium  than  white 
flour.  The  difference  in  calcium  content  between  the  whole 
grains  and  the  "  fine  "  mill  products,  while  not  so  great  as  in 
the  case  of  iron  or  phosphorus,  is  still  considerable.  In  general 
the  mining  removes  more  than  half  of  the  calcium.  The  fruits 
and  vegetables  in  general  are  fairly  rich  in  calcium,  while  some 
of  the  green  vegetables  are  strikingly  so ;  but  in  most  cases  the 
intake  of  calcium  depends  mainly  upon  the  extent  to  which 
milk  (and  its  products  other  than  butter)  enters  into  the  dietary. 
A  quart  of  milk  contains  rather  more  calcium  than  a  quart  of 
clear  saturated  lime  water.  By  far  the  most  practical  means 
of  insuring  an  abundance  of  calcium  in  the  dietary  is  to  use  milk 
freely  as  a  food. 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      269 


Approximate  Amounts  of  Calcium  in  Food  Material 


Food 


Beef,  all  lean 


Eggs  .     . 
Egg  yolk 


MUk 

Cheese    .... 
Wheat,  entire  grain 
White  flour      .     . 


Rice,  p>olished 
Oatmeal      .     , 


Beans,  dried 
Beets  .  . 
Cabbage  , 
Carrots  .  . 
Potatoes  . 
Turnips  .    . 


Apples    .    . 
Bananas 
Oranges 
Prunes,  dried 


Almonds 
Peanuts 
Walnuts 


Calcium 

Per  100  Grams 

Edible 

Substance 


grams 
0.007 


0.067 
0.137 

0.120 
0.931 
0.045  - 
0.020   i 

0.009  ' 

0.069 

0.160 

0.029 

0.04s  - 

0.056' 

0.014 

0.064 

0.007 
0.009 
0.045  - 
0.054 

0-239, 
0.071  • 
0.089 


Calcium 
Per  100 
Grams 
Protein 


grams 
0.03 

0.5 
0.9 

3-7 
3.5 
0.33 
0.18 

0.06 

0.4 

0.7 
1.9 
2.8 

5-1 
0.6 

5-0 

1.9 

0.7 
5-7 
2.6 

1.2 
0.3 
0.5 


Calcium 
Per  3000 
Calories 


grams 
0.18 

1-35 
I.I 

5.2 
6.4 
0.40 
0.18 

0.04 

0.5 

1.4 
1.9 
4-3 
3.7 
0.5 
4.8 

'O.36 
0.27 
2.6 
0.5 

I.I 

0.4 
0.4 


Relations  of  the  Inorganic  Elements  to  Each  Other 

It  is  evident  from  what  has  already  been  seen  that  the  custom 
which  has  been  more  or  less  prevalent  of  referring  to  the  ash  or 
mineral  matter  of  a  food  as  if  it  were  a  substance  is  wholly 


270  CHEMISTRY  OF  FOOD  AND  NUTRITION 

illogical  and  incorrect.  Food  ash  is  always  a  mixture  of  the  com- 
pounds of  several  different  elements,  and  each  element  has  its 
own  functions  and  significance  in  nutrition.  Even  elements 
so  closely  related  chemically  as  are  sodium  and  potassium,  or 
calcium  and  magnesium,  are  not  only  not  interchangeable,  but 
are,  in  some  of  their  functions,  directly  antagonistic  in  their 
action  in  the  body.  Bunge's  experiment  showing  the  effect 
of  potassium  upon  sodium  excretion  has  already  been  noted. 
Meltzer  and  his  associates  have  shown  that  the  injection  of 
magnesium  salts  has  a  marked  general  inhibitory  effect,  and  that 
this  can  be  quickly  overcome  by  the  subsequent  injection  of 
calcium  salt.  Summarizing  the  results  of  extended  series  of  in- 
vestigations by  himself  and  others,  Meltzer  stated,  in  the  Trans- 
actions of  the  Association  of  the  American  Physicians  for  1908  : 

"  Calcium  is  capable  of  correcting  the  disturbances  of  the 
inorganic  equilibrium  in  the  animal  body,  whatever  the  direc- 
tions of  the  deviations  from  the  normal  may  be.  Any  abnormal 
effect  which  sodium,  potassium,  or  magnesium  may  produce, 
whether  the  abnormality  be  in  the  .direction  of  increased  irrita- 
bility or  of  decreased  irritability,  calcium  is  capable  of  reestab- 
lishing the  normal  equilibrium." 

More  recently  Hart  and  Steenbock  have  found  that  the  ad-- 
dition  of  magnesium  salts  to  an  otherwise  well-balanced  ration 
tends  to  cause  a  loss  of  calcium  from  the  body.  Several  other 
observers  have  reported  similar  unfavorable  effects  of  magne- 
sium upon  the  metabolism  of  calcium,  and  some  are  inclined 
to  regard  this  as  a  matter  of  much  importance  to  the  well-being 
of  the  body.  On  the  other  hand,  calcium  seems  to  exert  a  favor- 
able influence  upon  the  economy  of  iron  in  metabolism,  inas- 
much as  it  appears  to  be  possible  to  maintain  equihbrium  upon 
a  smaller  amount  of  iron  when  the  food  contains  an  abundance 
of  calcium. 

It  would  thus  appear  that  an  adequate  study  of  the  subject 
should  take  account  of  the  relative,  as  well  as  the  absolute, 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      271 

amounts  of  the  different  inorganic  elements  of  the  food.  Tables 
showing  these  elements  for  the  different  articles  of  food  are  in- 
cluded in  the  Appendix  at  the  back  of  this  book.  Not  only 
do  the  different  food  materials  differ  greatly  in  the  absolute  and 
relative  abundance  of  the  different  elements,  but  the  same  is 
also  true  of  the  total  food  intake  of  different  groups  of  people. 
Studies  of  150  freely  chosen  American  dietaries  each  covering 
the  food  of  a  group  of  people  for  a  week  or  more  show  the  follow- 
ing range  and  average  intake,  per  man  per  day  and  per  3000 
Calories. 

Inorganic  Elements  in  150  American  Dietaries 


Per  Man  Per  Day 

Per  3000  Calories 

Min. 

Max. 

Average 

Min. 

Max. 

Average 

Calcium 
Magnesium 
Potassium 
Sodium 
Phosphorus 
Chlorine    . 
Sulphur     . 
Iron      .     . 

0.24 
0.14 

1.43 
0.19 
0.60 
0.88 
0.51 
0.0080 

1.87 
0.67 

6.54  , 

4.61 

2.79 

5.83 
2.82 
0.0307 

0.73 
0.34 
3-39 
1.94 

1.58 
2.83 
1.28 
0.0173 

0.35 
0.17 

1.63 

0,22 
0.72 
0.83 
0.80 
0.0090 

1-47 
0.53 
5-27 
4.83 
2.30 
7.26 

2.35 
0.0234 

0.73 
0.34 
3-40 
1-95 
1.59 
2.88 
1.30 
0.0174 

Since  these  dietary  records  did  not  show  the  quantities  of  salt 
used,  the  figures  for  sodium  and  chlorine  in  the  table  cover  only 
the  amounts  in  the  food  as  purchased  and  are  greatly  below  the 
actual  intake  of  these  elements.  It  will  be  seen  that  the  intake 
of  any  given  element  may  be  widely  different  in  the  different 
dietaries,  even  though  each  represents  the  daily  average  for 
at  least  a  week.  To  some  extent  this  is  due  to  the  variable 
amounts  of  total  food  consumed,  but  even  when  the  data  are 
reduced  to  a  uniform  basis  of  3000  Calories  the  differences  be- 
tween minimum  and  maximum  are  still  quite  wide. 


272 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


Output  of  Inorganic  Elements  during  Fasting 

In  view  of  the  relationships  discussed  above  it  is  of  interest 
to  examine  the  absolute  and  relative  excretion  of  the  different 
elements  as  recently  reported  by  Benedict  for  a  subject  who 
fasted  for  thirty-one  days. 

Urinary  Excretion  of  Different  Elements  during  a  31-DAY 
Fast  (Benedict) 


Day 

Nitrogen 

Chlo- 
rine 

Phos- 
phorus 

Sul- 
phur 

Calcium 

Magne- 
sium 

Potas- 
sium 

Sodium 

gms. 

gms. 

gms. 

gms. 

gms. 

gms. 

gms. 

gms. 

1 

7.10 

3.77 

0.73 

0.46 

0.217 

0.046 

1.630 

2.070 

2 

8.40 

1.02 

1.08 

0.61 

r.243 

.106 

1.368 

.926 

3 

11.34 

0.79 

1. 10 

0.68 

.243 

.106 

1.368 

.926 

4 

11.87 

0-59 

1.27 

0.67 

.•243 

.106 

1.368 

.926 

5 

10.41 

0.41 

I-I5 

0.65 

•274 

.098 

1.445 

.276 

6 

10.18 

0.40 

1.02 

0.65 

.274 

.098 

1-445 

.276 

7 

9-79 

0-S5 

0.80 

0.62 

•253 

.070 

.883 

.154 

8 

10.27 

0.32 

0.80 

0.64 

.253 

.070 

.883 

.154 

9 

10.74 

0.31 

0-93 

0.66 

.253 

.070 

.883 

.154 

10 

10.05 

0.28 

0.86 

0.61 

.220 

.072 

1.006 

.100 

II 

10.25 

0.36 

0.85 

0.62 

.220 

.072 

1.006 

.100 

12 

10.13 

0.31 

0.74 

0.62 

' 

216 

.065 

— 

— 

13 

10.35 

0.32 

0.85 

0.62 

.216 

.065 

— 

— 

14 

1043 

0.26 

0.81 

0.60 

1.236 

.071 

.814 

.109 

15 

8.46 

0.16 

0.64 

0.50 

.236 

.071 

.814 

.109 

16 

9.58 

0.14 

0.89 

0-S9 

.214 

.078 

— 

— 

17 

8.81 

0.12 

0.87 

0-53 

.214 

.078 

— 

— 

18 

8.27 

0-15 

0.81 

O.S4 

.251 

.059 

.676 

.051 

^9,-. 

8.37 

0.16 

0.77 

o.SS 

.251 

.059 

.676 

.051 

20 

7.69 

0.15 

0.64 

0.51 

.237 

•053 

•644 

.066 

21 

7.93 

0.18 

0.70 

o.Si 

.237 

.053 

.644 

.066 

22 

7-75 

0.21 

0.69 

0.50 

.179 

.050 

.643 

.083 

23 

7.31 

0.18 

0.71 

0.51 

.179 

.050 

.643 

.083 

24 

8.15 

O.IO 

0.68 

0.49 

.167 

,056 

.787 

.065 

25 

7.81 

0.18 

0.67 

0.49 

.167 

.056 

.787 

.065 

26 

7.88 

0.16 

0.65 

O.S4 

•153 

.051 

.656 

.055 

27 

8.07 

0.16 

0.62 

0.52 

•153 

•051 

.656 

.055 

28 

7.62 

0.14 

0.59 

0.53 

.131 

.047 

.585 

.036 

29 

7-54 

0.12 

0.64 

0.52 

.131 

.047 

.585 

.036 

30 

7.83 

0.14 

0.61 

0.52 

.138 

.052 

.606 

.053 

31 

6.94 

0.13 

0.58 

0.49 

[.138 

.052 

.606 

.053 

INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      273 

It  will  be  noted  that  the  nitrogen  output  and  the  output  of 
chlorine  run  entirely  different  courses,  especially  in  the  eariy 
days  of  the  fast.  Each  of  the  other  elements  seems  to  run  its 
own  course  except  that  the  sulphur  tends  to  remain  relatively 
constant  Hke  the  nitrogen  (both  being  derived  from  protein 
metabolism),  and  the  output  of  sodium  tends  to  run  parallel 
with  that  of  chlorine,  since  these  two  elements  are  excreted 
mainly  in  combination  with  each  other  as  common  salt. 

The  Maintenance  of  Neutrality  in  the  Body 

One  of  the  interesting  relationships  among  the  ash  constit- 
uents of  foods  is  that  between  the  acid-forming  and  the  base- 
forming  elements,  since  this  has  a  direct  bearing  upon  the  im- 
portant problem  of  the  maintenance  of  neutrality  in  the  body. 

Although  the  reaction  of  normal  human  blood  is  alkaline  to 
litmus,  the  actual  excess  of  hydroxyl  over  hydrogen  ions  is 
found  by  modern  methods  to  be  so  sHght  that  blood  as  well  as 
protoplasm  is  commonly  spoken  of  as  neutral.  Thus  Henderson 
writes :  "  NeutraHty  is  a  definite,  fundamental,  and  important 
characteristic  of  the  organism." 

The  normal  processes  of  metabolism,  however,  involve  a  contin- 
ual production  of  acid  (chiefly  carbonic,  phosphoric,  and  sulphuric) 
which  must  be  disposed  of  in  order  to  maintain  this  neutrahty. 

The  factors  generally  recognized  as  concerned  in  the  main- 
tenance of  neutrality  are:  (i)  carbonates,  (2)  phosphates, 
(3)  ammonia,  (4)  proteins. 

As  preliminary  to  even  a  brief  mention  of  the  function  of  these 
different  mechanisms  for  maintaining  neutrality,  it  may  be  well 
to  recur  for  a  moment  to  the  fundamental  conceptions  which  have 
recently  been  so  well  summarized  by  Henderson  as  follows :  * 

"  First,  the  product  of  the  concentrations  of  hydrogen  and  hy- 
droxyl ions  (at  constant  temperature)  is  approximately  constant. 
(H+)  .  (0H-)  =  c 

*  Science,  Vol.  46,  page  78  (July  27,  191 7). 
T 


274  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Therefore  the  concentrations  of  these  two  ions  always  vary 
inversely 

^      ^       (0H-) 

"  Secondly,  if  for  convenience,  just  as  the  histologist  uses  mi- 
crons instead  of  meters,  we  adopt  as  unit  concentrations  of 
hydrogen  and  hydroxyl  ions  a  very  small  quantity,  viz.  the 
concentration  of  these  ions  in  neutral  solutions,  the  value  of 
this  constant  becomes  unity.* 

(H+)  .  (0H-)  =  I, 
I 


(H+)  = 


(0H-) 

It  may  be  noted  that,  using  this  unit  of  concentration,  an  ordi- 
nary decinormal  solution  of  hydrochloric  acid  has  a  concentra- 
tion of  hydrogen  ions  of  nearly  1,000,000;  and  a  decinormal 
solution  of  sodium  hydroxide,  a  corresponding  concentration  of 
hydroxyl  ions. 

"  Thirdly,  upon  this  basis  the  definitions  of  neutrality,  acid- 
ity, and  alkalinity  are  as  follows : 

For  neutrahty, 

(H^)  =  I  =  (0H-) 


For  acidity, 
For  alkalinity. 


(H^)  >  I  >  (0H-) 


(H+)  <  I  <  (0H-) 

"  Finally,  in  any  solution  containing  a  weak  acid  and  its  salts 
with  one  or  more  bases,  regardless  of  the  other  components  of 
the  solution,  the  concentration  of  hydrogen  ions  is  approxi- 
mately proportional  to  the  ratio  of  free  acid  to  combined  acid. 

*  The  more  usual  method  of  expressing  hydrogen  ion  concentration  has  been 
referred  to  in  an  earlier  chapter  (page  77). 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      275 

This  relation,  however,  holds  only  when  the  ratio  of  acid  to  salt 
is  neither  very  large  nor  very  small. 

"  It  is  therefore  evident  that  in  the  solution  of  any  weak  acid, 
when  the  quantities  of  free  and  combined  acid  are  equal,  the 
value  of  (H+)  is  y^ ;  if  the  ratio  of  acid  to  salt  be  10 :  i,  (H"*")  is 
10  k,  if  the  ratio  be  i :  10,  (H"^)  is  o.i  ^." 

In  the  case  of  carbonic  acid  and  of  acid  phosphates  the  value 
of  k  is  near  enough  to  unity  so  that  solutions  containing  acid 
carbonate  or  a  mixture  of  primary  and  secondary  phosphates 
must  always  remain  nearly  neutral. 

Carbonic  acid  produced  in  metabohsm  is  chiefly  disposed 
of  by  eHmination  as  carbon  dioxide  through  the  lungs.  For 
description  of  the  mechanism  and  regulation  of  carbon 
dioxide  elimination  the  reader  must  be  referred  to  discus- 
sions of  the  physiology  of  respiration.  Its  bearing  upon 
the  problem  of  neutrality  is  summarized  by  Henderson  as 
follows : 

'*  This  substance  is  the  chief  excretory  product  of  the  organism. 
As  such  it  must  be  eUminated  promptly  and  completely.  More- 
over, in  that  it  leaves  the  body  not  in  aqueous  solution  and  as 
an  acid,  but  almost  exclusively  in  the  form  of  gaseous  carbon 
dioxide,  there  is  no  possibility  of  any  variation  of  the  permanent 
effect  produced  upon  the  reaction  of  the  body  by  the  elimina- 
tion of  a  definite  amount  of  it.  In  the  final  regulation  by  ex- 
cretion it  is  not,  therefore,  concerned.  And  yet  it  has,  in  the 
process  of  excretion,  a  very  important  role  in  regulating  the 
reaction  of  the  body.  This  depends  upon  the  fact  that  carbonic 
acid  is  not  only  a  waste  product,  but  also  a  normal  constituent 
of  the  blood,  and,  as  such,  a  principal  factor  in  the  physico- 
chemical  regulation.  Thus,  if  the  ratio  of  carbonic  acid  to 
bicarbonates  in  a  normal  individual  were  i :  15,  a  large  produc- 
tion of  acid  might  cause  a  destruction  of  a  third  part  of  all  the 
bicarbonates,  producing  in  its  place  an  equivalent  amount  of 
free  carbonic  acid.    This,  if  nothing  else  occurred,  would  reduce 


276  CHEMISTRY  OF  FOOD  AND  NUTRITION 

the  relative  amount  of  bicarbonates  from  15  to  10,  and  simul- 
taneously increase  the  free  carbonic  acid  from  i  to  6.  The  ratio 
would  now  be  6 :  10,  and  since  the  hydrogen  ion  concentration 
is  proportional  to  this  ratio,  this  ion  would  suffer  a  nearly  ten- 
fold increase  of  concentration.  But  at  this  point,  or,  more 
strictly  speaking,  continuously  during  the  process,  the  excretory 
function  intervenes.  There  is  a  tendency  for  the  respiratory 
process  to  hold  the  tension  of  carbon  dioxide  in  the  blood 
nearly  constant.  This  is  the  reason  why  carbonic  acid  has  some- 
times been  thought  the  respiratory  hormone.  Assuming  that 
the  exact  quantity  of  carbonic  acid  set  free  by  the  reaction  of 
neutralization  were  thus  eliminated,  the  ratio  would  be  reduced 
to  1 :  10,  and  the  hydrogen  ion  concentration  would  rise  but  one 
third  above  its  original  value.  More  recent  investigations, 
however,  have  shown  that  a  tendency  to  acidity  is  accomplished 
by  a  lowering  of  the  tension  of  carbon  dioxide.  Let  us  suppose 
that  in  this  case  the  tension  was  lowered  one  third.  The  free 
carbonic  acid  of  the  blood  would  then  become  0.67  instead  of 
1. 00,  and  the  ratio  of  acid  to  salt  0.67:  10,  which  is  exactly 
equal  to  i:  15,  the  original  ratio.  Accordingly,  the  hydrogen 
ion  concentration  would  be  restored  exactly  to  its  original  value, 
and  the  regulation  by  excretion  would  be  quite  perfect.  Now 
there  is  abundant  evidence  to  show  that  something  very  much 
like  this  is  always  occurring  in  the  body,  and,  on  the  whole,  I 
believe  that  the  most  delicate  of  all  means  to  regulate  the  reac- 
tion of  the  body  is  to  be  found  in  this  variation  of  the  tension 
of  carbonic  acid  during  its  excretion.  Such  considerations  have 
strengthened  the  hypothesis  that  the  hydrogen  ion  is  the  true 
respiratory  hormone."     (Henderson,  loc.  cit.) 

Phosphates  are  regularly  present  in  blood  and  urine  in  no- 
table amounts.  From  what  has  already  been  seen  regarding 
the  reaction  of  the  blood,  it  may  be  inferred  that  in  it  the  primary 
and  secondary  phosphates  are  normally  present  in  such  pro- 
portions as  to  produce  a  practically  neutral  mixture.    In  urine, 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      277 

on  the  other  hand,  acid  phosphate  predominates,  because  the 
kidney  usually  removes  from  the  blood  a  larger  proportion  of 
primary  than  of  secondary  phosphate.  Thus  by  virtue  of  this 
ability  of  the  kidney  to  secrete  an  acid  urine  from  a  neutral 
blood,  the  excess  of  phosphoric  acid  produced  in  metabolism 
is  readily  disposed  of.  The  disposal  of  the  sulphuric  acid  pro- 
duced in  the  metabolism  of  protein  is  a  more  complicated  prob- 
lem. Sulphuric  is  so  strong  an  acid  that  it  would  soon  poison 
the  body  unless  quickly  neutraUzed. 

When  a  fairly  strong  acid  such  as  the  sulphuric  acid  produced 
in  the  metabolism  of  protein  enters  a  neutral  or  slightly  alkaline 
solution  of  phosphates  and  carbonates  such  as  the  blood,  it 
reacts  with  secondary  phosphate  to  form  primary  phosphate 
and  with  bicarbonate  to  form  carbonic  acid.  Since  secondary 
phosphate  (K2HPO4  or  Na2HP04)  is  but  faintly  basic,  and  pri- 
mary phosphate  (KH2PO4  or  NaH2P04)  is  but  faintly  acid,  the 
ratio  of  these  phosphates  may  be  considerably  changed  {i.e.  a 
considerable  amount  of  strong  acid  may  be  received  by  the 
phosphate  mixture)  without  appreciably  diminishing  the  alka- 
Hnity  of  the  solution.  Thus  the  blood  may  neutralize  a  con- 
siderable amount  of  acid  without  appreciable  change  in  its  reac- 
tion, or  as  ordinarily  expressed,  without  alteration  of  its  own 
neutrality.* 

*  This  property  is  also  referred  to  as  the  "buflfer  effect"  of  phosphate  solutions 
and  is  of  course  connected  with  the  capacity  for  secondary  ionization,  readily  re- 
versible according  to  the  reaction  of  the  medium : 

Acid  Alkaline 

H3PO4  ^  H2PO4-  ^  HP04=  ^  P04= 

or 
H8FO4  ±  H2PO4-  +  H+ 

HP04=  +  H+ 

P04^  +  H+    ^ 
For  discussion  of  acid-base  equilibria  in  phosphate  solutions  see  the  works  of 
Henderson  cited  at  the  end  of  the  chapter. 


278  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Ammonia,  which  is  continually  being  formed  in  the  body  by 
deaminization  of  amino  acids  in  the  course  of  protein  metabo- 
lism, constitutes  another  means  of  neutralization  of  acid.  It 
will  be  remembered  that,  according  as  more  or  less  acid  is  formed 
in,  or  introduced  into,  the  body,  a  larger  or  smaller  proportion  of 
the  nitrogen  eliminated  appears  in  the  urine  as  ammonium  salts.* 

Proteins,  such  as  those  of  blood  serum,  are  amphoteric  sub- 
stances and  can  unite  with  acid  by  virtue  of  their  amino,  and 
perhaps  other  basic,  groups.  The  constant  presence  of  pro- 
teins in  all  parts  of  the  body  constitutes,  therefore,  a  further 
mechanism  for  the  immediate  fixation  of  any  strong  acid  pro- 
duced. This,  however,  is  only  a  temporary  and  partial  solution 
of  the  problem,  since  the  acid  thus  fixed  would  remain  to  be  dis- 
posed of  when  the  protein  is  hydrolyzed  to  amino  acids. 

The  relations  of  these  different  factors  in  the  maintenance 
of  neutrality  under  normal  conditions  are  summarized  by  Hen- 
derson as  follows :  f 

-  '*  The  hydrogen  ion  concentration  of  the  body  has  been  seen 
to  depend  on  the  ratio 

H2CO3 
NaHCOs 

Acid  reacting  with  this  system  causes  a  diminution  of  the  de- 
nominator and  an  increase  in  the  numerator  of  the  fraction,  the 
value  of  the  fraction  increases,  and  with  it  the  hydrogen  ion 
concentration.  Hereupon  the  lung  reduces  the  value  of  the 
numerator  by  diminishing  the  concentration  of  carbon  dioxide 
in  blood  and  alveolar  air,  the  value  of  the  fraction  is  restored 

*  Two  facts  should,  however,  be  kept  in  mind  as  possibly  limiting  the  utility  of 
this  means  of  disposing  of  acid.  In  the  first  place,  ammonium  salts  are  generally 
regarded  as  somewhat  toxic,  their  accumulation  in  the  body  being  normally  pre- 
vented by  conversion  into  urea.  Secondly,  there  is  no  good  reason  to  suppose  that 
the  deaminization  processes  which  form  ammonia  will  always  go  on  in  the  same 
cells  and  at  the  same  time  with  the  oxidation  processes  which  produce  sulphuric 
acid. 

t  Loc.  cit.,  page  81.    j 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      279 

more  or  less  exactly  to  its  original  value  and  with  it  the  concen- 
tration of  the  hydrogen  ion.  But  the  denominator  is  still  below 
normal.  To  offset  this,  there  occurs,  on  the  one  hand,  a  pro- 
duction of  ammonia  which  takes  the  place  in  the  urine  of  alkaU 
existing  as  salt  in  the  blood.  This  alkali  recombines  with  car- 
bonic acid,  forming  bicarbonate,  and  thus  increasing  the  de- 
nominator. On  the  other  hand  the  kidney  removes  less  alkali 
in  combination  with  phosphates  than  exist  in  this  state  in  the 
blood.  This  alkaK,  too,  helps  to  regenerate  sodium  bicarbonate, 
and  thus  to  increase  the  denominator.  Both  of  these  processes 
are  so  regulated  that  the  denominator  is  restored  to  normal. 
The  concentration  of  carbonic  acid  responds  through  the  ac- 
tivity of  the  respiratory  mechanism,  and  the  organism  returns 
to  its  normal  state. 

*'  These  processes,  of  course,  go  on  simultaneously  and  not  in 
succession.  They  are,  moreover,  far  less  simple  than  such  an 
analysis  admits,  for  on  the  one  hand  the  interaction  of  phos- 
phates and  proteins  has  not  been  fully  described,  and,  on  the 
other  hand,  many  of  these  variations  influence  other  conditions 
and  processes  in  the  organism." 

The  normal  fluctuations  of  fixed  acid  production  in  healthy 
man  on  ordinary  mixed  diet  are  apparently  taken  care  of  in 
part  by  neutraHzation  with  ammonia  and  in  part  by  the  forma- 
tion and  excretion  of  acid  phosphate.  In  an  experiment  upon 
man  by  Gettler  and  the  writer  it  was  found  that,  of  the  extra 
acid  formed  in  metaboUsm  as  the  result  of  replacing  the  potato 
of  a  mixed  diet  by  rice,  about  33  per  cent  was  accounted  for 
by  the  increased  ammonia  and  about  40  per  cent  by  the  in- 
creased acidity  of  the  urine,  leaving  a  remainder  which  may  have 
been  eliminated,  in  part  at  least,  through  the  skin,  since  no 
attempt  was  made  to  measure  the  amount  or  acidity  of  the  per- 
spiration, or  may  have  been  neutralized  by  sodium  or  potassium 
carbonate  in  the  blood  or  other  fixed  alkali  from  the  body.  In 
this  experiment  the  intake  and  output  of  phosphorus  was  ap- 


28o  CHEMISTRY  OF  FOOD  AND  NUTRITION 

proximately  the  same  on  both  diets.  The  increased  acidity  of 
the  urine,  therefore,  impHed  an  increased  ratio  of  primary  to 
secondary  phosphate  in  the  urine  but  not  necessarily  any  in- 
crease in  the  amount  of  fixed  base  leaving  the  body.  In  the 
neutralization  of  sulphuric  acid  by  means  of  phosphate,  each 
molecule  of  hydrogen  sulphate  (representing  one  atom  of  sul- 
phur oxidized  in  protein  metabolism)  changes  two  molecules 
of  secondary  into  primary  phosphate.  In  order  that  the  orig- 
inal condition  of  equilibrium  may  continue,  the  surplus  acid 
phosphate  thus  formed  must  be  excreted.  Whether  or  not 
this  results  in  an  increased  excretion  of  phosphates  and  there- 
fore of  sodium  or  potassium  (or  only,  as  in  the  experiment  just 
cited,  an  altered  ratio  of  primary  and  secondary  phosphates  in 
the  urine),  apparently  depends  not  only  upon  the  balance  of 
acid-forming  and  base-forming  elements  in  the  food,  but  also 
upon  the  quantities  of  fixed  bases  and  of  phosphates  which  are 
being  metabolized  and  of  ammonia  available  from  the  protein 
metabohsm.  It  would  seem  that  in  any  case  in  which  sulphuric 
acid  produced  in  metabolism  is  neutralized  by  the  sodium  or 
potassium  carbonate  of  the  blood,  the  resulting  sulphate  must  be 
eliminated  with  corresponding  loss  of  sodium  or  potassium  and 
decrease  of  the  capacity  of  the  blood  for  combining  with  carbon 
dioxide.  This  is  an  important  feature  of  acidosis.  It  is  diag- 
nosed by  determining  the  carbon-dioxide-holding  capacity  of 
a  sample  of  blood  serum  and  the  result  is  expressed  as  the 
"  alkali  reserve  "  or  "  reserve  alkalinity  "  of  the  blood. 

Thus  while  the  phosphates  and  carbonates  of  the  blood  and 
tissues  serve  for  the  immediate  neutralization  of  acid  without 
appreciable  change  in  the  normal  reaction  of  the  blood  or  tissue 
itself,  yet  when  much  strong  acid  such  as  the  sulphuric  acid 
from  protein  metabolism  is  neutralized  in  this  way,  there  is  apt 
to  result  an  increased  output  of  the  base-forming  elements, 
which  if  not  made  good  by  the  intake  must  tend  to  diminish 
the  ''  reserve  alkalinity  "  or  "  alkali  reserve  "  of  the  body. 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      281 

That  an  excess  of  acid-forming  elements  in  food,  even  if  long 
continued,  does  not  necessarily  lead  to  any  apparent  injury  is 
shown  by  experiments  of  McCoUum,  in  which  rats  were  main- 
tained throughout  a  large  part  of  their  adult  lives  and  produced 
healthy  young  on  a  diet  of  egg-yolk,  in  which  there  is  a  great 
predominance  of  acid-forming  over  base-forming  elements.  Yet 
in  man  an  increase  in  the  ammonia  content  and  acidity  of 
the  urine  is  usually  regarded  (if  pronounced  and  persistent) 
as  indicating  an  unfavorable  tendency.  In  this  connection 
the  decreased  uric  acid  solvent  power  of  the  more  acid  urine 
is  to  be  considered,  especially  in  view  of  the  present  beHef  that 
the  human  organism  does  not  destroy  uric  acid  but  must  trans- 
port and  excrete  all  that  is  produced  in  the  body.  Hindhede  * 
found  that  the  eating  of  vegetables,  particularly  potatoes,  in- 
creases the  capacity  of  the  urine  for  dissolving  uric  acid.  Fur- 
thermore, Hasselbalch  f  showed  that  the  carbon  dioxide  tension 
of  the  alveolar  (expired)  air,  which  is  indicative  of  the  carbon- 
dioxide-carrying  capacity  and  therefore  of  the  reserve  alka- 
linity of  the  blood,  is  influenced  in  a  similar  way  by  the  food. 
On  a  diet  rich  in  meat  he  found  a  tension  of  37.8  mm. ;  on  an 
ordinary  mixed  diet,  38.3  mm. ;  on  a  vegetarian  diet,  43.3  mm. 

In  an  extended  series  of  experiments,  Blatherwick  J  Hkewise 
finds  that  foods  which  have  a  preponderance  of  base-forming 
elements  lead  to  the  formation  of  a  urine  which  is  less  acid, 
both  as  regards  hydrogen  ion  concentration  and  titration 
acidity,  and  which  has  an  increased  capacity  for  dissolving  uric 
acid,  while  the  ammonia  content  of  the  urine  is  diminished  and 
the  carbon  dioxide  tension  of  the  alveolar  air,  indicative  of 
reserve  alkalinity,  is  increased.  Conversely,  foods  with  a 
predominance  of  acid-forming  elements  increase  the  urinary 
acidity  and  urinary  ammonia,  decrease  the  uric  acid  solvent 

*  Skandinavisches  Archivfiir  Physiologie,  Vol.  26,  pages  87,  384  (1912). 

t  Biochemisches  Zeitschrift,  Vol.  46,  page  403  (191 2). 

X  Archives  oj  Internal  Medicine,  Vol.  14,  pages  409-50  (1914)- 


282  CHEMISTRY  OF  FOOD  AND  NUTRITION 

power,  and  show,  through  lowered  carbon  dioxide  tension  of 
the  alveolar  air,  a  tendency  toward  depletion  of  the  reserve 
alkalinity  of  the  blood. 

The  benefit  to  health  which  so  generally  results  from  a  free 
use  of  milk,  vegetables,  and  fruits  in  the  diet  may  be  attributable 
in  part  to  the  fact  that  these  foods  yield  alkaHne  residues  when 
oxidized  in  the  body ;  but  this  point  should  not  be  too  greatly 
emphasized,  for  there  are  several  other  respects  in  which  the 
eating  of  Hberal  amounts  of  milk,  vegetables,  and  fruits  is 
certainly  beneficial,  notably  in  supplying  calcium,  iron,  and 
vitamines,  and  in  improving  the  intestinal  conditions. 

REFERENCES 

(See  also  the  references  at  the  end  of  Chapter  IX.) 

Aron.  Calcium  Requirement  of  Children  (and  the  Relation  of  Calcium 
Metabolism  to  Rickets).  Biochemisches  Zeitschrift,  Vol.  12,  page  28 
(1908). 

Aron  and  Frese.  Utilization  of  Different  Forms  of  Food-Calcium  in  the 
Growing  Organism.     Biochemisches  Zeitschrift,  Vol.  9,  page  185  (1908). 

Aron  and  Sebauer.  Importance  of  Calcium  for  the  Growing  Organism. 
Biochemisches  Zeitschrift,  Vol.  8,  page  i  (1908). 

Benedict.  A  Study  of  Prolonged  Fasting.  Carnegie  Institution  of  Wash- 
ington, Publication  No.  203,  page  247  (191 5). 

Blather  WICK.  Foods  in  Relation  to  the  Composition  of  the  Urine.  Ar- 
chives of  Internal  Medicine,  Vol.  14,  page  409  (19 14). 

Blauberg.  Mineral  Metabolism  of  Infants.  Zeitschrift  fiir  Biologic,  Vol. 
40  (N.  S.  22),  pages  i,  36  (1900). 

Camerer  and  Soldner.  Ash  Constituents  of  the  New  Born  Infant  and  of 
Human  Milk.     Zeitschrift  fur  Biologic,  Vol.  44  (N.  S.  26),  page  61  (1903). 

DiBBELT.  Significance  of  Calcium  Salts  during  Pregnancy  and  Lactation 
and  the  Influence  of  a  Loss  of  Calcium  upon  Mother  and  Offspring. 
Beitrdge  pathologische  Anatomic  (Zeigler),  Vol.  48,  page  147  (1910). 

EvvARD,  Dox,  AND  GUERNSEY.  Effect  of  Calcium  and  Protein  Fed  Preg- 
nant Swine  upon  the  Size,  Vigor,  Bone, 'Coat,  and  Condition  of  the 
Offspring.     American  Journal  of  Physiology,  Vol.  34,  page  312  (1914). 

FiTZ,  Alsberg,  and  Henderson.  Concerning  the  Excretion  of  Phosphoric 
Acid  during  Experimental  Acidosis  in  Rabbits.  American  Journal  of 
'Physiology,  Vol.  18,  page  113  (1907). 


INORGANIC  FOODSTUFFS  AND  MINERAL  METABOLISM      283 

Forbes.    The  Balance  between  Inorganic  Acids  and  Bases  in  Animal 

Nutrition.     Ohio  Agricultural  Experiment  Station,  Bulletin  207  (1909). 
Forbes.     The  Mineral  Nutrients  in  Practical  Human  Dietetics.     Scientific 

Monthly,  Vol.  2,  page  282  (1916). 
Forbes  and  Beegle.    The  Mineral  Metabolism  of  the  Milch  Cow.    Ohio 

Agricultural  Experiment  Station,  Bulletin  295. 
Givens  and  Mendel.     Studies  in  Calcium  and  Magnesium  Metabolism. 

Journal  of  Biological  Chemistry,  Vol.  31,  pages  421,  435,  441  (1917). 
Hart  and  Steenbock.     The  Effect  of  High  Magnesium  Intake  on  Calcium 

Retention  by  Swine.     Journal  of  Biological  Chemistry,  Vol.  14,  page 

75  (1913)- 
Hent)ERSON.     The  Fitness  of  the  Environment. 
Henderson.     Equilibrium  in  Solutions  of  Phosphates.     American  Journal 

of  Physiology,  Vol.  15,  page  257  (1906). 
Henderson.     A  Critical  Study  of  the  Process  of  Acid  Excretion.     Journal 

of  Biological  Chemistry,  Vol.  9,  page  403  (191 1). 
Henderson.     The  Regulation  of  Neutrality  in  the  Animal  Body.     Science^ 

Vol.  37,  page  389  (March  14,  1913). 
Henderson.     The   Excretion  of  Acid  in  Health  and  Disease.     Harvey 

Society  Lectures  for  1914-1915. 
Henderson.     Acidosis.     Science,  Vol.  46,  page  73  (191 7). 
Kastle.     On  the  Available  Alkali  in  the  Ash  of  Human  and  Cow's  Milk 

and  its  Relation  to  Infant  Nutrition.     American  Journal  of  Physiology, 

Vol.  22,  page  284  (1908). 
LusK.     Science  of  Nutrition,  3d  edition,  pages  215-222,  358-361. 
Mathews.     Physiological  Chemistry. 
McCoLLUM  AND  HoAGLANT).     The  Effect  of  Acid  and  Basic  Salts  and  of 

Free  Mineral  Acids  on  the  Endogenous  Nitrogen  Metabolism.    Journal 

of  Biological  Chemistry,  Vol.  16,  page  299  (19 13). 
MiCHAELis.     Die  Wasserstaffion-concentration. 
Nelson  and  Williams.    The  Urinary  and  Fecal  Output  of  Calcium  in 

Normal  Men.    Journal   of  Biological    Chemistry,  Vol.   28,  page   231 

(1916). 
Osborne.     Sulphur  in  Proteins.    Journal  of  the  American  Chemical  Society, 

Vol.  24,  page  140  (1902). 
Robertson.     On  the  Nature  of  the  Chemical  Mechanism  which  Maintains 

the  Neutrality  of  the  Tissues  and  Tissue  Fluids.    Journal  of  Biological 

Chemistry,  Vol.  6,  page  313  (1909). 
Sherman  and  Gettler.    The  Balance  of  Acid-forming  and  Base-forming 

Elements  in  Foods  and  its  Relation  to  Ammonia  Metabolism.     Journal 

of  Biological  Chemistry,  Vol.  11,  page  323  (1912). 


284  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Steenbock,  Nelson,  and  Hart.  Acidosis  in  Omnivora  and  Herbivora 
and  its  Relation  to  Protein  Storage.  Journal  of  Biological  Chemistry, 
Vol.  19,  page  399  (1914)- 

Steenbock  and  Hart.  Influence  of  Function  on  the  Lime  Requirement 
of  Animals.    Journal  of  Biological  Chemistry,  Vol.  14,  page  59  (1913). 

Stoeltzner.  The  Two-fold  Significance  of  Calcium  in  the  Growth  of  Bone. 
Archiv  fur  die  gesamle  Physiologic  (PJluger),  Vol.  122,  page  599  (1908). 

Tangl.  The  Metabolism  of  an  Artificially  Fed  Child.  Ibid.,  Vol.  104, 
page  453  (1904). 

Tigerstedt.  Ash  Content  of  the  Ordinary  Dietary  of  Man.  Skandina- 
visches  Archiv  fiir  Physiologic,  Vol.  24,  page  97  (191 1). 

Underhill.  Studies  on  the  Metabolism  of  Ammonium  Salts.  Journal  of 
Biological  Chemistry,  Vol.  15,  pages  327,  337,  341  (19I3). 

Van  Slyke,  Cullen,  Stillman,  and  Fitz.  (Acid  Excretion  and  the  Alka- 
line Reserve.)  Proceedings  of  the  Society  of  Experimental  Biology  and 
Medicine,  Vol.  12,  pages  165,  184  (1915);  Journal  of  Biological  Chem- 
istry, Vol.  30,  pages  289,  347,  369,  389,  401,  405  (1917)- 

VoiT  (E.).  Significance  of  Calcium  in  Animal  Nutrition.  Zeitschrift  fiir 
Biologie,  Vol.  16,  page  55  (1880). 


CHAPTER  XI 
IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION 

The  amount  of  iron  contained  in  the  body  is  small,  but  its 
functions  are  of  the  highest  importance.  As  previously  noted, 
the  iron  content  of  the  adult  man  or  woman  is  estimated  at 
only  0.004  per  cent,  or  i  part  in  25,000  parts  of  the  body  weight, 
or  rather  less  than  3  grams  (hardly  one  tenth  of  an  ounce)  in 
the  entire  body.  Much  the  greater  part  of  this  iron  exists  as  a 
constituent  of  the  hemoglobin  of  red  blood  corpuscles  and  is 
constantly  functioning  in  the  general  metabolism  as  the  carrier 
of  the  oxygen  upon  which  all  of  the  oxidative  (energy-yielding) 
processes  of  nutrition  depend.  There  is  no  considerable  reserve 
store  of  relatively  inactive  iron  in  the  body  corresponding  to 
the  store  of  calcium  and  phosphorus  in  the  bones.  Hence  if 
the  intake  of  iron  fails  to  equal  the  output  there  must  soon  result 
a  diminution  of  hemoglobin,  which  if  continued  must  mean  a 
greater  or  less  degree  of  anemia.  The  investigation  of  iron 
metabolism  has  therefore  been  largely  connected  with  the 
study  of  anemia  and  of  hemoglobin  formation. 

Important  changes  of  view  in  regard  to  the  metabolism  of 
iron  have  followed  so  closely  and  have  depended  so  directly  upon 
the  progress  of  experimental  methods  that  it  seems  desirable, 
in,  this  case,  to  review  in  chronological  order  some  of  the  more 
important  steps  in  the  development  of  our  present  knowledge. 

Development  of  Modem  Views 

It  has  long  been  known  that  iron  is  essential  to  the  nutrition 
of  both  plants  and  animals,  and  that  small  amounts  of  the  oxide 

28s 


286  CHEMISTRY  OF  FOOD  AND   NUTRITION 

or  phosphate  of  iron  occur  in  the  ash  of  all  natural  food  materials. 
A  few  decades  ago  it  was  assumed  that  the  iron  exists  in  the  food 
as  oxide  or  phosphate,  and  that  hemoglobin  is  formed  in  the 
body  by  the  combination  of  protein  with  inorganic  iron.  This 
view  was  hardly  consistent  with  the  ideas  of  animal  metabolism 
taught  by  Liebig  and  generally  held  at  the  time,  but  appeared 
to  be  supported  by  the  successful  use  of  inorganic  iron  in  the 
treatment  of  anemia. 

The  results  obtained  in  a  number  of  investigations  published 
between  1854  and  1884  threw  doubt  upon  the  utilization  of  in- 
organic iron  for  the  production  of  hemoglobin,  since  they  indi- 
cated that  iron  salts  when  injected  act  as  poisons  and  are 
quickly  eliminated  from  the  blood,  and  when  given  by  the 
mouth  reappear  almost  quantitatively  in  the  feces,  httle,  if 
any,  evidence  of  absorption  being  obtained  except  when  the 
doses  were  so  large  or  long  continued  as  to  cause  irritation  of 
the  intestine. 

In  the  attempt  to  harmonize  this  result  with  clinical  ex- 
perience it  was  suggested  that  the  inorganic  iron  might  act 
by  absorbing  the  hydrogen  sulphide  of  the  intestine,  thus 
protecting  the  food  iron  from  waste. 

The  view  that  medicinal  iron  acts  by  stimulation  of  the 
absorbing  membrane  was  also  advocated  at  about  this 
time.  It  was  held  that  the  amount  of  iron  in  the  ordinary 
food  is  always  sufficient  for  the  needs  of  the  body,  but  that 
sometimes  the  intestinal  mucous  membrane  becomes  so  blood- 
less that  it  cannot  properly  perform  its  functions  of  absorp- 
tion. Under  such  conditions  inorganic  iron  was  believed  to 
stimulate  and  tone  up  the  membrane  so  that  in  a  short  time 
the  increased  absorption  of  food  iron  makes  good  the  defi- 
ciency in  the  blood. 

A  very  suggestive  discussion  of  the  metabolism  of  iron, 
the  effects  of  a  lack  of  iron  in  the  food,  and  the  amounts  of 
iron  required  for  the  maintenance  of  the  body  in  health  was 


IRON  IN  FOOD  AND   ITS   FUNCTIONS  IN  NUTRITION      287 

published  by  Von  Hosslin  in  1882,  and  long  before  this  some 
attention  had  been  given  to  the  iron  content  of  food  materials 
by  Boussingault.  Boussingault's  figures,  however,  are  not 
sufficiently  accurate  to  be  of  value  at  the  present  time,  and 
little  attention  was  given  to  the  subject  discussed  by  Von 
Hosslin  until  it  was  reopened  by  Bunge  about  two  years  later. 

Bunge,  in  1884,  doubting  the  abiHty  of  the  animal  body  to 
form  hemoglobin  from  inorganic  iron,  undertook  the  study  of 
the  iron  compounds  of  food  materials  in  order  to  find  in  what 
form  iron  is  normally  absorbed  and  from  what  sort  of  iron  com- 
pounds the  growing  organism  ordinarily  forms  its  hemoglobin. 
Practically  all  of  the  iron  of  eggs  was  found  to  be  in  the  yolk. 
Yolk  of  egg  does  not  contain  any  hemoglobin,  but  it  must  con- 
tain substances  from  which  hemoglobin  can  be  formed,  since 
the  incubation  of  the  egg  results  in  the  development  of  hemo- 
globin without  the  introduction  of  anything  from  without. 
Bunge  found  no  inorganic  iron  in  egg  yolk,  but  isolated  con- 
siderable amounts  of  the  precursor  of  hemoglobin,  which  he 
called  "  hematogen,"  and  which  exhibited  the  properties  of  a 
phosphoprotein  containing  about  0.3  per  cent  of  iron  in  such 
firm  "  organic  "  combination  that  it  gives  none  of  the  ordinary 
reactions  of  iron  salts.  In  milk,  cereals,  and  legumes  similar 
organic  compounds  of  iron  and  only  traces  of  inorganic  iron 
were  found.  At  this  time  Bunge  distinctly  stated  that  iron 
occurs  in  food  solely  in  the  form  of  compHcated  organic  com- 
pounds which  have  been  built  up  by  the  life  processes  of  plants. 
In  this  form,  said  Bunge,  is  the  iron  absorbed  and  assimilated, 
and  from  these  compounds  hemoglobin  is  produced. 

In  1890  and  subsequently,  the  absorption  and  assimi- 
lation of  iron  was  studied  by  several  experimenters,  usually 
with  particular  reference  to  the  question  whether  inorganic 
or  synthetic  organic  compounds  of  iron  are  absorbed  and 
assimilated,  and  especially  whether  such  preparations  contribute 
directly  to  the  formation  of  hemoglobin.     This  question  is,  of 


288  CHEMISTRY  OF  FOOD  AND   NUTRITION 

course,  extremely  impdrtant,  not  only  in  connection  with  the 
therapeutic  use  of  medicinal  iron,  but  also  in  its  bearing  upon 
the  iron  requirements  in  health;  for  if  inorganic  iron  could  be 
utilized  in  the  body  in  exactly  the  same  way  as  the  complex 
organic  iron  compounds  of  the  food,  it  would  follow  that  the 
iron  of  drinking  water  could  replace  that  of  food,  and  the  supply- 
ing of  food  iron  would  be  a  matter  of  indifference  to  a  man  whose 
drinking  water  suppHed  a  few  milligrams  of  iron  per  day.  In 
opposition  to  this  view,  Bunge  held  that  little  if  any  inorganic 
iron  is  assimilated,  and  that  any  effect  of  medicinal  iron  should 
be  attributed  to  its  action  in  protecting  the  food  iron  from  loss 
in  digestion,  principally  by  absorbing  the  sulphur  liberated  as 
sulphide  through  intestinal  putrefaction. 

Socin  demonstrated  the  superiority  of  the  iron  of  egg  yolk 
over  iron  chloride  by  dividing  a  number  of  mice  into  groups, 
some  of  which  were  fed  on  a  mixture  of  iron-free  food  and  iron 
chloride,  while  others  received  the  same  iron-free  food  with  the 
addition  of  egg  yolk.  None  of  the  mice  fed  without  organic 
iron  lived  for  more  than  thirty-two  days,  while  some  of  those 
receiving  egg  yolk  Hved  as  long  as  the  experiments  were  con- 
tinued (sixty  to  ninety-nine  days),  and  gained  in  weight. 

Gottlieb,  recognizing  the  fact  that  iron  might  be  absorbed 
and  used  by  the  body,  yet  finally  excreted  with  the  feces, 
determined  the  intestinal  elimination  of  iron  in  dogs  before 
and  after  subcutaneous  and  intravenous  injections  of  known 
amounts  of  iron  salts.  From  the  results  obtained  it  was  esti- 
mated that  practically  all  of  the  injected  iron  was  eliminated 
by  the  intestines. 

Voit  studied  the  metabolism  of  iron  in  dogs  by  direct  ob- 
servations of  absorption  and  elimination  in  isolated  sections 
of  the  small  intestine.  Opening  the  peritoneal  cavity,  he 
separated  the  desired  section,  removed  the  contents,  closed 
the  ends,  and  left  the  sac  thus  formed  in  its  normal  position 
after  having  reunited  the  remainder  of  the  intestine.     Under 


IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION      289 

these  conditions  the  isolated  section  of  intestine,  while  not 
coming  in  direct  contact  with  anything  taken  by  the  mouth, 
would  still  receive  its  proportional  share  of  anything  eHm- 
inated  from  the  body  through  the  intestinal  wall.  By  kill- 
ing and  examining  animals  which  had  been  kept  for  some 
time  after  such  an  operation,  Voit  was  able  to  compare  the 
amount  of  iron  eliminated  through  the  intestinal  wall  with 
the  amounts  contained  in  food  and  feces,  and  thus  to  infer 
the  extent  to  which  the  iron  taken  by  the  mouth  was  ab- 
sorbed and  returned  to  the  intestine  for  elimination.  In 
fasting,  the  daily  elimination  found  for  each  square  meter 
of  intestinal  surface  was  6  milligrams  in  the  feces  and  the 
same  amount  (per  square  meter  of  surface)  in  the  isolated 
loop  of  intestine.  On  food  poor  in  iron  the  feces  contained 
in  each  of  two  cases  10  milHgrams,  the  isolated  loops  6  and 
9  milligrams,  of  iron  per  square  meter  of  intestinal  surface; 
while  on  food  rich  in  iron  the  corresponding  figures  for  two 
experiments  were  43  and  78  milligrams  in  the  feces,  and  8 
and  6  milligrams  in  the  isolated  portion  of  the  intestine. 
Hence  it  appears  that  the  iron  eliminated  in  the  feces  during 
fasting  or  on  food  poor  in  iron  came  from  the  body  through 
the  intestinal  wall,  while  most  of  the  extra  iron  given  with 
the  food  in  the  last  two  experiments  passed  through  the  al- 
imentary canal  without  being  absorbed  and  metabolized. 

Stockman,  in  a  paper  upon  the  metabolism  of  iron,  pub- 
lished in  1893,  while  discussing  mainly  the  therapeutics  of 
chlorosis  (a  type  of  anemia  occurring  in  girls  and  young  women) 
undertook  to  solve  the  question  of  the  absorption  of  inorganic 
iron.    He  reasoned  as  follows : 

If  inorganic  iron  preparations  given  hypodermically  will 
cure  chlorosis,  there  can  in  such  cases  be  no  possibihty  of  the 
iron  exerting  its  effect  by  the  stimulation  of  the  ahmentary 
canal  or  by  combining  with  hydrogen  sulphide  in  the  intestine. 

If  iron  sulphide  given  by  the  mouth  cures  chlorosis,  it  must 
u 


290  CHEMISTRY  OF  FOOD  AND  NUTRITION 

be  through  absorption  of  the  iron,  since  ferrous  sulphide  has 
no  stimulating  effect  and  cannot  take  up  more  sulphur. 

If  bismuth,  manganese,  etc.,  take  up  hydrogen  sulphide 
as  readily  as  iron,  but  are  inert  in  chlorosis,  a  further  indirect 
evidence  of  absorption  of  iron  is  obtained. 

Stockman  made  experiments  and  observations  upon  hos- 
pital patients  (of  which  he  cites  nine  cases)  which  appeared 
to  substantiate  each  of  the  three  propositions,  and  thus  to 
estabhsh  the  fact  that  inorganic  iron  preparations  cure  chlorosis 
through  being  absorbed  and  utilized  in  the  formation  of  hemo- 
globin. 

During  the  years  1 894-1 897  several  investigators  studied 
the  absorption  of  different  forms  of  iron  by  microchemical 
methods.  Suitable  stains  having  been  found  for  the  iden- 
tification of  iron  in  the  microscopic  sections  of  tissue,  it  was 
possible  by  exarnination  of  the  intestinal  wall  and  the  various 
organs  and  tissues  of  the  body  to  follow  the  absorption,  storage, 
and  elimination  of  the  iron  given  medicinally  or  occurring  in 
the  food.  Macallum  investigated  in  this  manner  the  behavior, 
of  inorganic  salts  of  iron,  iron  albuminates,  and  the  iron  com- 
pound of  the  egg  yolk,  and  found  that  iron  taken  in  any  of  these 
forms  may  be  absorbed  from  the  small  intestine. 

Woltering  compared  microchemically  and  by  quantitative 
determination  the  amounts  of  iron  in  the  livers  of  mice,  rabbits, 
and  dogs,  fed  with  and  without  sulphate  of  iron,  and  reported 
an  increase  in  the  iron  content  of  the  liver  and  in  the  hemoglobin 
and  red  corpuscles  of  the  blood  as  the  result  of  feeding  the  iron  salt. 

Gaule,  using  principally  microchemical  methods,  found 
no  reaction  for  iron  in  the  chyle  under  normal  conditions ; 
but  a  distinct  reaction  appeared  in  the  lymph  nodes,  and 
extended  to  the  spleen  soon  after  the  feeding^  of  iron  salt  to 
rabbits.  This  absorption  of  inorganic  iron  was  followed  by 
an  increase  in  the  number  of  red  corpuscles  and  percentage  of 
hemoglobin  in  the  blood. 


IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION      291 

In  the  meantime,  Kunkel  and  Egers  studied  especially 
the  influence  of  iron  salts  upon  the  regeneration  of  blood 
after  hemorrhage.  Kunkel  kept  two  dogs  on  a  limited  milk 
diet,  but  gave  one  of  them,  in  addition  to  the  milk,  iron  in 
the  form  of  albuminate.  Each  of  the  animals  was  bled 
every  seven  days,  about  one  third  of  the  total  blood  being 
taken  each  time.  The  iron  in  the  drawn  blood  was  deter- 
mined and  ascertained  to  be  greater  than  the  amount  sup- 
plied by  the  milk,  but  less  than  the  total  iron  received  by 
the  dog  which  was  fed  with  albuminate.  The  experiment 
was  continued  seven  weeks,  at  the  end  of  which  time  the 
blood  and  organs  of  the  dog  which  had  been  kept  on  milk 
alone  were  poorer  in  iron  than  those  of  the  dog  which  had 
received  the  iron  albuminate.  Only  one  animal  was  fed  in 
each  way,  and  no  determinations  of  hemoglobin  are  recorded. 
According  to  Egers,  the  regeneration  of  blood  after  severe 
losses  (one  third  of  the  estimated  total)  is  very  slow  on  food 
poor  in  iron,  unless  medicinal  iron  is  also  given,  when  the 
rate  of  regeneration  becomes  better,  but  not  so  good  as  on 
a  diet  supplying  an  abundance  of  food  iron  alone.  Even 
when  the  diet  was  rich  in  food  iron,  however,  Egers  found 
that  medicinal  iron  appeared  to  aid  the  regeneration  of  blood 
after  hemorrhage. 

These  investigations  having  shown  that  inorganic  iron  is  at 
least  to  some  extent  absorbed  and  carried  to  organs  which  take 
part  in  the  production  of  hemoglobin,  it  became  of  especial  im- 
portance to  determine  by  long-continued  feeding  experiments 
whether  the  inorganic  iron  thus  absorbed  can  take  the  place  of 
food  iron  in  the  production  of  hemoglobin  under  normal  condi- 
tions. 

This  question  was  studied  by  Hausermann  in  an  extended 
series  of  experiments  in  Bunge's  laboratory.  The  general 
plan  of  these  experiments  was  to  feed  young  animals  from 
the  end  of  the  normal  suckling  period  upon  food  poor  in  iron, 


292  CHEMISTRY  OF  FOOD  AND  NUTRITION 

usually  milk  and  rice.  One  half  of  the  animals,  however, 
received  ferric  chloride  in  addition  to  this  food.  After  the 
animals  had  been  thus  fed  for  from  one  to  three  months  and 
had  usually  doubled  in  weight,  they  were  killed,  and  the  amount 
of  hemoglobin  in  the  entire  body  was  estimated;  also,  in 
the  case  of  small  animals,  the  total  amount  of  iron.  Ex- 
periments were  carried  out  in  this  way  upon  24  rats,  17 
rabbits,  and  14  dogs.  The  results  are  summarized  essentially 
as  follows  by  Bunge :  * 

The  rats  all  became  highly  anemic,  for  at  the  end  of  the 
experiment  the  percentage  of  hemoglobin  was  diminished 
to  about  half  that  of  animals  from  the  same  Htter  which  had 
received  their  normal  food,  namely,  meat,  flies,  yolk  of  egg, 
fruit,  and  vegetables.  The  rats  which  had  taken  ferric 
chloride  in  addition  to  the  milk  and  rice  contained  no  more 
hemoglobin  than  those  which  had  received  milk  and  rice 
only.  Moreover,  the  amount  of  iron  was  in  each  case  the 
same.  In  one  experiment  alone,  in  which  the  addition  of 
ferric  chloride  was  continued  for  three  months,  was  the 
iron  found  to  be  double  as  much  in  the  animals  which  had 
received  it  as  in  those  which  had  only  milk  and  rice.  But 
here  again  the  proportion  of  hemoglobin  remained  the  same 
in  both  instances.  We  thus  see  that  some  iron  is  absorbed 
if  small  doses  of  iron  are  persisted  in  for  a  long  time,  as  well 
as  if  large  amounts  be  suddenly  administered.  But  this 
inorganic  iron,  when  absorbed,  is  not  utiHzed  In  the  for- 
mation of  hemoglobin  to  any  appreciable  extent,  but  remains 
unused  in  the  tissues.  Whether  inorganic  iron  was  absorbed  in 
the  experiments  which  lasted  only  from  one  to  two  months  can- 
not be  decided ;  it  is  possible  that  some  of  it  was  absorbed  and 
was  again  eliminated  in  the  same  degree.  Certainly  no  storing 
up  nor  increase  of  iron  could  be  detected  in  the  whole  organism. 

*  Physiological  and  Pathological  Chemistry,  Blakiston's  edition.  Philadelphia, 
1902,  page  379. 


IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION       293 

The  experiments  on  rabbits  gave  less  decisive  results.  The 
average  proportion  of  hemoglobin  in  the  animals  that  received 
inorganic  iron  was  somewhat  higher  than  that  in  the  animals 
which  were  fed  on  milk  and  rice  only.  But  when  the  great 
individual  differences  between  various  animals  are  taken  into 
consideration,  too  much  importance  must  not  be  ascribed  to  this 
slight  divergence.  At  any  rate,  the*  amount  of  hemoglobin  in 
the  control  animal,  which  received  its  normal  diet  —  fresh 
green  cabbage,  bran,  etc.  —  was  nearly  twice  as  high  as  in  the 
animal  which  received  the  inorganic  iron. 

The  experiments  upon  dogs  were  not  attended  with  decisive 
results,  as  dogs  are  not  suitable  animals  for  these  experiments, 
owing  to  the  variation  in  individuals.  Moreover,  the  growth 
of  these  animals  after  the  period  of  lactation  is  at  a  much  slower 
rate,  and  their  appetite  is  so  enormous  that  they  might  readily 
be  able  to  assimilate  sufficient  iron  for  hemoglobin  formation 
even  from  a  material  so  poor  in  iron  as  milk.  In  fact,  Hauser- 
mann  found  the  largest  proportion  of  hemoglobin  in  a  dog 
which  had  been  fed  exclusively  upon  milk.  The  animals  which 
received  ferric  chloride  in  addition  to  a  milk  diet  certainly  con- 
tained no  more  hemoglobin  than  animals  from  the  same  litter 
which  were  fed  on  meat  and  bones. 

Abderhalden,  following  Hausermann,  studied  the  subject 
even  more  exhaustively.  *  In  order  to  ascertain  whether  and 
to  what  extent  sulphides  normally  exist  in  the  alimentary 
canal,  —  a  question  of  special  importance  in  connection  with 
one  view  of  the  mode  of  action  of  inorganic  iron,  —  Abder- 
halden killed  and  examined  rats,  mice,  cats,  dogs,  guinea 
pigs,  and  rabbits  in  the  following  way:  Immediately  upon 
killing  the  animal,  the  abdomen  was  opened  and  the  intestinal 
tract  from  the  esophagus  to  the  rectum  was  ligated  in  sections. 
The  contents  of  each  section  were  then  removed  and  tested 
qualitatively  for  sulphides.  Hydrogeh  sulphide  was  obtained 
from  the  contents  of  the  large  intestine,  but  not  from  those 


294  CHEMISTRY  OF  FOOD  AND  NUTRITION 

of  the  small  intestine  nor  of  the  stomach.  Hence,  if  in- 
organic iron  acts  by  improving  the  absorption  of  food  iron, 
it  must  do  so  in  some  other  way  than  by  simply  preventing 
its  precipitation  as  sulphide,  since  this  would  not  occur  in  the 
small  intestine,  where  the  principal  absorption  of  iron  takes 
place.  The  next  step  in  the  investigation  was  to  study  by 
microchemical  methods  the  absorption  of  inorganic  iron,  its 
behavior  in  the  body,  and  its  elimination.  Experiments 
were  made  upon  49  rats  from  7  litters,  14  guinea  pigs  from 
6  litters,  12  rabbits  from  2  litters,  10  dogs  from  3  litters,  and 
6  cats  from  2  litters. 

From  all  of  these  experiments,  Abderhalden  concluded 
that  the  compHcated  iron  compounds  of  the  normal  food, 
the  iron  in  the  form  of  hemoglobin,  and  hematin,  and  the 
inorganic  iron,  were  all  absorbed  in  the  same  general  way, 
stored  in  the  same  organs,  and  eliminated  by  the  same  paths. 

In  studying  the  utilization  by  the  body  of  the  different 
forms  of  iron,  Abderhalden  fed  animals  from  the  end  of  the 
suckhng  period,  or,  in  the  case  of  guinea  pig,  from  birth,  on 
food  poor  in  iron,  and  divided  each  litter  into  two  groups, 
one  of  which  was  given  inorganic  iron  in  addition.  After  a 
sufficient  time  the  animals  were  killed,  and  the  total  hemo- 
globin in  the  body  of  each  was  estimated.  Experiments  of 
this  kind  were  made  upon  48  rats,  44  rabbits,  14  guinea  pigs, 
17  cats,  and  11  dogs.  The  animals  fed  with  food  poor  in  iron 
plus  an  addition  of  inorganic  iron  were  unable  to  produce  as 
much  hemoglobin  as  those  receiving  normal  food. 

In  these  experiments,  Abderhalden  had  noticed  some  facts 
which  indicated  that  the  favorable  influence  of  inorganic 
iron  upon  metabolism  and  blood  formation  was  greater  on 
a  diet  rich  in  food  iron  than  when  the  amount  of  food  iron 
was  kept  small.  In  order  to  test  this,  experiments  were  made 
with  66  rats,  10  rabbits,  and  14  guinea  pigs,  in  the  manner 
already  described,  but  with  diets  arranged  to  bring  out  this 


IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION      295 

particular  point.  These  experiments  led  to  the  conclusion  that 
the  greater  the  quantity  of  food  iron  present,  the  greater  the 
influence  of  the  inorganic  iron  upon  the  hemoglobin  formation. 

Abderhalden's  experiments  also  showed  that  the  production 
of  hemoglobin  was  not  stimulated  indefinitely  by  inorganic 
iron,  but  only  for  a  short  time,  and  he  concluded  that,  while 
inorganic  iron  may  be  absorbed  and  may  favorably  influence 
blood  formation,  it  is  not  used  as  material  for  the  production  of 
hemoglobin.  It  has  also  been  found  clinically  that  medicinal 
iron  gives  better  results  when  used  intermittently  than  when 
used  continuously,  which  indicates  that  the  action  is  due  to 
stimulation  rather  than  to  the  inorganic  iron  actually  going  to 
form  hemoglobin. 

The  results  obtained  by  Tartakowsky  *  were  more  favorable 
to  the  view  that  hemoglobin  may  be  formed  from  inorganic 
iron.  He  found  that  young  growing  animals  fed  on  rice  and 
milk  gradually  became  anemic  and  finally  ceased  to  grow ;  but 
that  when  inorganic  iron  was  added  to  the  rice-milk  diet  the 
blood  regained  its  normal  iron  content  and  the  animal  soon 
began  to  grow  again.  From  such  experiments  together  with  a 
large  number  of  microchemical  observations,  Tartakowsky 
concludes  that  medicinal  (inorganic)  iron  is  assimilated  like 
food  iron  and  serves  in  the  same  way  for  the  production  of 
hemoglobin  and  the  other  organic  iron  compounds  of  the  body. 
He  further  insists  that  Abderhalden's  experiments  should  also 
be  interpreted  in  the  same  way,  since  in  many  cases  the  animals 
which  received  inorganic  iron  in  addition  to  their  food  formed 
more  hemoglobin  than  the  control  animals. 

More  recently,  Schmidt  f  has  described  some  interesting 
experiments  upon  mice  with  a  similar  iron-poor  rice-and-milk 
diet.     According  to  Schmidt  this  diet  did  not  cause  anemia 

*  Archiv  fur  die  gesamte  Physiologic,  Vol.  100,  page  586;  Vol.  loi,  page  423 
(1903,  1904). 

t  Verhandlungen  der  Deuisches  Pathologisches  Gesellschaft,  Vol.  15,  page  91  (191 2). 


296  CHEMISTRY  OF  FOOD  AND  NUTRITION 

in  adult  mice ;  but  the  offspring  of  mice  which  had  been  kept 
on  such  diet  seemed  to  lack  the  normal  reserve  store  of  iron,  and 
by  continuing  the  milk-rice  diet  to  the  third  generation  there 
were  obtained  what  this  investigator  describes  as  "  iron-free 
families  '.'  of  mice.  In  these  the  red  blood  cells  were  very  poor 
in  hemoglobin.  From  such  a  family  of  mice  two  sisters  seven 
months  old  were  selected ;  one  was  continued  on  the  milk-rice 
diet  alone  while  the  other  was  fed  medicinal  iron  (Ferrum  oxyda- 
tum  saccharatum)  in  addition  for  eleven  days ;  then  both  were 
killed  and  examined.  The  first  showed  the  typical  anemic 
condition  of  these  "  iron-free  famihes,"  the  hemoglobin  number 
and  number  of  red  blood  cells  being  both  less  than  half  of  the 
normal ;  while  in  the  second  mouse,  which  had  received  medicinal 
iron  for  eleven  days,  the  hemoglobin  number  and  number  of  red 
blood  cells  were  both  about  twice  as  high  as  in  the  first.  This  is 
held  by  Schmidt  to  show  that  medicinal  iron  does  not  merely 
stimulate  the  blood-forming  organs  to  greater  activity  but  does 
itself  enter  into  hemoglobin  formation. 

It  is  difficult  to  determine  how  much  weight  should  be  given 
to  the  findings  of  Tartakowsky  and  of  Schmidt  as  opposed  to 
the  more  extended  and  more  quantitative  experiments  of  Hauser- 
mann  and  of  Abderhalden. 

While  it  cannot  yet  be  stated  positively  that  inorganic  iron 
is  or  is  not  used  by  the  animal  body  as  material  for  the  pro- 
duction of  hemoglobin,  the  best  medical  opinion  appears  to 
support  the  conclusion  reached  by  Abderhalden,  that  hemo- 
globin is  derived  essentially  from  the  organic  iron  compounds 
of  the  food,  while  inorganic  iron  acts  mainly  if  not  entirely  as 
a  stimulus.  This  view  is  strongly  supported  by  Von  Noorden 
in  his  treatise  on  chlorosis  in  Nothnagel's  Encyclopedia  of 
Practical  Medicine,  and  Ehrlich  and  Lazarus,  writing  on  anemia 
in  the  same  work,  state : 

"  It  is  not  very  probable  that  the  (medicinal)  iron  stored  by  the 
liver  and  spleen  is  directly  employed  in  the  formation  of  hemo- 


IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION       297 

globin ;  on  the  contrary,  the  assumption  first  suggested  by  Von 
Noorden  seems  much  more  plausible,  namely,  that  the  iron  exer- 
cises a  direct  irritative  action  on.  the  function  of  the  blood-making 
organs." 

The  Iron  Requirement  of  the  Body 

A  very  brief  summary  of  the  leading  facts  regarding  the 
normal  nutritive  relations  of  iron  may  well  precede  the  dis- 
cussion of  the  amount  required. 

Iron  is  an  essential  element  of  hemoglobin  and  of  the  chro- 
matin substances,  i.e.  of  the  body  constituents  most  directly 
concerned  with  the  processes  of  oxidation,  secretion,  reproduc- 
tion, and  development.  The  substances  thus  fundamentally 
connected  with  metabolism  processes  contain  their  iron  in 
firm  organic  combination,  as  a  constituent  of  their  charac- 
teristic proteins;  and  the  normal  materials  for  the  production 
of  these  body  constituents  are  the  similar  iron-protein  com- 
pounds of  the  food. 

The  iron  of  the  food  is  absorbed  from  the  small  intestine, 
enters  the  circulation  by  way  of  the  lymph,  and  is  deposited 
mainly  in  the  liver,  spleen,  and  bone  marrow.  Its  final  ehm- 
ination  takes  place  mainly  through  the  walls  of  the  intestines. 

Both  inorganic  and  synthetically  prepared  organic  forms 
of  iron  are  absorbed  from  the  same  part  of  the  digestive 
tract,  stored  in  the  same  organs,  and  eliminated  by  the  same 
paths  as  the  iron  of  the  food.  These  medicinal  forms  of  iron 
often  stimulate  the  production  of  hemoglobin  and  red  blood 
corpuscles. 

Whether  medicinal  iron  actually  serves  as  material  for  the 
construction  of  hemoglobin  is  not  positively  known,  but  we 
have  what  appears  to  be  good  evidence  that  food  iron  is 
assimilated  and  used  for  growth  and  for  the  regeneration  of 
hemoglobin  to  much  better  advantage  than  are  inorganic  or 
synthetic  forms,  and  that  when  medicinal  iron  increases  the 


298  CHEMISTRY  OF  FOOD  AND   NUTRITION 

production  of  hemoglobin,  its  effect  is  more  beneficial  in  pro- 
portion as  the  food  iron  is  more  abundant  —  a  strong  indica- 
tion that  the  medicinal  iron  acts  by  stimulation  rather  than  as 
material  for  the  construction  of  hemoglobin. 

Evidently,  then,  we  should  look  to  the  food  rather  than  to 
medicines  or  mineral  waters  for  the  supply  of  iron  needed  in 
normal  nutrition. 

Comparatively  few  experiments  upon  the  amount  of  food 
iron  required  for  the  maintenance  of  equihbrium  in  man  have 
been  made.  Cetti  and  Breithaupt  eliminated  0.0073  and 
0.0077  gram  per  day,  respectively,  when  fasting.  Three  men 
observed  by  Stockman  while  receiving  in  the  food  about 
0.006  gram  each  per  day  eliminated  0.0063,  o-oo93j  ^-nd  0.0115 
gram,  respectively.  Von  Wendt  found  his  requirements  to 
range  in  a  number  of  experiments  on  different  diets  from  0.008 
to  0.016  gram  per  day,  the  largest  amount  being  required  in  a 
case  where  the  diet  was  deficient  in  calcium.  In  three  experi- 
ments by  Sherman  in  which  the  food  contained  0.0057  to  0.0071 
gram  of  iron  there  was  metabolized  0.0055,  0.0087,  ^-nd  0.0126 
gram  per  day,  respectively,  and  here  also  the  amount  of  iron 
which  sufficed  for  equiHbrium  when  taken  in  the  form  of  bread 
and  milk  (a  diet  rich  in  calcium)  was  insufficient  when  taken  in 
the  form  of  a  diet  (poor  in  calcium)  consisting  of  bread  and  egg 
white,  or  bread  alone.  In  this  case,  however,  the  difference 
in  the  economy  of  the  metabolism  of  the  iron  may  have  been  due 
not  simply  to  the  change  in  the  calcium  content  of  the  food,  but 
also  to  a  superior  nutritive  value  of  the  iron  compounds  of  milk 
over  those  of  bread  and  to  the  fact  that  the  general  conditions  of 
digestion  and  nutrition  were  better  when  milk  was  included  in 
the  diet  than  when  it  was  excluded.  The  nitrogen,  phosphorus, 
calcium,  and  iron  balances  for  two  of  these  experiments  per- 
formed upon  the  same  man  and  with  diets  practically  alike  in 
energy  value  and  protein  content,  are  shown  in  the  following 
table ; 


IRON  IN  FOOD  AND  ITS   FUNCTIONS  IN  NUTRITION       299 
Comparison  of  Balances  of  Different  Elements 


Nature  of 
Element 

Amount  in  Grams  per  Day 

Nature  of  Diet 

In  food 

In  feces 

In  urine 

Balance 

Bread  and  milk     .     . 
Bread  and  egg  white . 

Nitrogen 
Nitrogen 

10.10 
10.69 

0.46 
0.75 

13.09 
13.21 

-3-45 

-  3.27 

Bread  and  milk      .     . 
Bread  and  egg  white  . 

Phosphorus 
Phosphorus 

1-55 
0.38 

0.57 
0.22 

1.03 
0.75 

—  0.05 
-0.59 

Bread  and  milk      .     . 
Bread  and  egg  white 

Calcium 
Calcium 

1.89 
o.io 

1-34 
0-34 

0.15 
0.07 

+  0.40 
-0.31 

Bread  and  milk      .     . 
Bread  and  egg  white  . 

Iron 
Iron 

0.0057 
0.0065 

•0053 
.0085 

.0002 
.0002 

+    .0002 
—    .0022 

Here,  although  the  nitrogen  balance  was  practically  alike 
on  the  two  diets,  there  was  on  the  bread  and  milk  diet  prac- 
tical equilibrium  of  phosphorus  and  iron  and  a  storage  of 
calcium,  while  on  the  diet  of  bread  and  egg  white  there  were 
noteworthy  losses  of  all  three  of  these  elements. 

Returning  to  the  problem  of  the  quantitative  determination 
of  the  iron  requirement  it  will  be  seen  that  in  the  cases  in  which 
the  intake  and  output  of  iron  have  been  determined,  the  require- 
ment appears  to  have  varied  with  individuals  and  with  the 
nature  of  the  diet  from  0.006  to  0.016  gram  (6  to  16  milligrams)  of 
iron  per  man  per  day. 

We  might  conclude  from  these  results  that  a  daily  allow- 
ance of  10  to  12  miUigrams  of  food  iron  should  suffice  for  the 
maintenance  of  iron  equilibrium  in  an  averagfe  man  under 
favorable  conditions,  but  until  the  conditions  which  deter- 
mine a  larger  metabolism  of  iron  are  more  clearly  defined,  it 
would  seem  desirable  to  set  a  higher  standard,  perhaps  15 
milligrams  of  food  iron  per  man  per  day. 

In  calculating  the  iron  requirement  for  a  family  dietary,  it 


300  CHEMISTRY  OF  FOOD  AND   NUTRITION 

is  well  to  make  the  allowance  for  women  and  children  more 
liberal  than  would  be  indicated  by  their  total  food  require- 
ment. A  woman  requiring  eight  tenths  as  much  food  as  a 
man  will  probably  require  more  than  eight  tenths  as  much 
iron,  and  a  child  requiring  half  as  much  food  may  easily  re- 
quire more  than  half  as  much  iron;  for  the  influence  of 
menstruation,  pregnancy,  and  lactation  in  women  and  of 
growth  and  development  in  children  may  reasonably  be  ex- 
pected to  affect  the  demand  for  iron  to  an  even  greater  extent 
than  they  affect  the  requirement  for  total  food.  It  is  probable 
that  pregnancy  and  lactation  increase  the  iron  requirement 
of  the  mother  by  at  least  3  milligrams  per  day,  and  al  other 
times  the  losses  of  blood  in  menstruation  must  call  for  a  greater 
intake  of  iron  than  would  be  needed  by  a  healthy  man  of  equal 
energy  and  protein  requirement. 

Since  milk  is  the  sole  food  of  young  mammals  during  a 
considerable  period  of  rapid  growth,  Bunge  was  surprised  to 
find  only  small  amounts  of  iron  in  milk  ash.  Comparing 
the  composition  of  the  ash  of  milk  with  that  of  the  newborn 
animals  of  the  same  species,  it  was  found  that,  while  other 
constituents  occurred  in  nearly  the  same  relative  proportions, 
the  iron  was  six  times  as  abundant  in  the  ash  of  the  young 
animal  as  in  that  of  the  milk  on  which  it  was  nourished.  That 
the  suckling  animal  grows  rapidly  and  increases  its  blood 
supply  in  spite  of  this  apparent  deficiency  of  iron  in  its  food  is 
due  to  the  fact  that  the  body  contains  a  reserve  supply  of  iron 
at  birth.  In  confirmation  of  this  statement  Bunge  and  his  pupils 
have  published  many  analyses  showing  that  the  percentage  of 
iron  in  the  entire  organism  is  highest  at  birth,  and  that  during 
the  suckling  period  the  amount  of  iron  in  the  body  remains 
about  constant,  notwithstanding  the  increase  in  body  weight. 

In  all  cases  in  which  the  young  depend  entirely  upon  the 
milk  of  the  mother  during  the  suckling  period  the  body  con- 
stituents- of   the  young  must  evidently  be  derived  entirely 


IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION      301 

from  the  maternal  organism  either  before  birth  through  the 
placenta  or  after  birth  through  the  milk  glands  of  the  mother 
and  the  digestive  tract  of  the  young.  Since  disordered  diges- 
tion may  readily  lead  to  defective  absorption  of  the  iron  of 
the  food,  nature  apparently  takes  the  precaution  of  conveying 
the  necessary  iron  from  mother  to  offspring  mainly  by  the 
safer  method,  i.e.  through  the  placenta.  Hence  in  the  ease  of 
animals  which  feed  solely  upon  milk  for  some  time  after  birth, 
a  relatively  large  amount  of  iron  is  stored  before  birth  for  use 
in  the  formation  of  hemoglobin  during  the  suckling  period.  This 
has  been  shown  by  analysis  to  be  true  of  children,  puppies, 
kittens,  and  rabbits.  On  the  other  hand,  guinea  pigs,  which  feed 
on  green  leaves  or  other  food  rich  in  iron  from  the  first  day  of 
life,  are  born  without  this  reserve  store  of  iron  (Bunge).  From 
recent  analyses  it  appears  that  the  percentage  of  iron  in  the 
human  body  is  about  three  times  as  high  at  birth  as  at  maturity. 
If  it  be  assumed,  as  indicated  by  Bunge's  work,  that  during  the 
milk  feeding  of  infancy  the  amount  of  iron  in  the  body  remains 
about  constant,  it  would  follow  that  the  percentage  of  iron  in  the 
child's  body  would  be  reduced  to  that  in  the  adult  when  the  body 
weight  becomes  about  three  times  what  it  was  at  birth  —  usu- 
ally when  a  little  over  one  year  old,  —  and  that  from  this  time 
on  throughout  the  period  of  growth,  care  should  be  taken  that 
the  food  is  sufficiently  rich  in  iron  to  provide  not  only  for 
equilibrium,  but  also  for  the  constantly  increasing  blood  supply. 

Iron  in  Foods 

Little  weight  can  be  attached  to  such  statements  regarding 
the  iron  content  of  foods  as  are  based  upon  the  data  obtain- 
able from  the  ordinary  tables  of  ash  analyses,  since  these  have 
usually  been  obtained  by  methods  which  are  likely  to  greatly 
overestimate  the  amount  of  iron.  In  the  following  table 
are  shown  the  approximate  amounts  of  iron  now  believed  to 
be  present  in  the  average  edible  portion  of  typical  food  materials 


302 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


expressed  (i)  in  milligrams  per  loo  grams  of  edible  material, 
(2)  in  milligrams  per  100  grams  of  protein,  (3)  in  milligrams 
per  3000  Calories: 


Iron  in  Typical  Food  Materials 


Food 


Beef,  all  lean  .  .  . 
Beefsteak,  medium  fat 

Eggs 

Egg  yolk  .... 
Milk,  whole  .  .  . 
Milk,  skimmed     .     . 

Cheese 

Oatmeal  .... 
Rice,  polished  .  . 
White  flour  .  .  . 
Wheat,  entire  grain  . 
Beans,  dried  .  .  . 
Beans,  string,  fresh  . 

Beets 

Cabbage     .... 

Carrots 

Corn,  sweet  .  .  . 
Peas,  dried  .  .  . 
Potatoes  .... 
Spinach  ..... 
Turnips       .... 

Apples 

Bananas  .... 
Oranges  .... 
Prunes,  dried  .  .  . 
Almonds     .     .     .     . 

Peanuts 

Walnuts      .... 


Iron  per  too 
Grams  Fresh  Sub- 
stance, Milli- 
grams 


3.8s 

2.2 

3.0 

8.6 

0.24 

0.25  ^ 

1-3 

3.8 

0.9 

i.o 

S-o 

7.0 

I.I  — 

0.6 

I.I  — 

0.6  -^ 

0.8 

5-7 

1.3 

3.6- 

o-S 

0.3 

0.6 

0.2 

3-0 

3.9 

2.0 

2.1 


Iron  per  icxj 

Grams  Protein, 

Milligrams 


16 

16 

22 

53 

7 

7 

5 

22 
II 
7 
37 
40 
48 
38 
69 
55 
26 

23 
55 

135 
39 
78 
47 
25 

143 
19 


Iron  per  3000 
Calories,  Milli- 
grams 


97 
47 
57 
^9 
10 
20 

9 

26 

7 

7 

42 

60 

80 

39 

104 

40 

23 
46 
42 

450 
38 
15 
18 
12 
30 
18 
II 
9 


Percentages  of  iron  in  some  other  foods  will  be  found  in  the 
tables  of  ash  constituents  in  the  Appendix.  Using  these  recent 
data  for  iron  in  food  materials,  approximate  estimates  of  the 


IRON  IN   FOOD   AND   ITS   FUNCTIONS  IN  NUTRITION      303 

amounts  of  iron  contained  in  150  American  dietaries  have  been 
made.  The  majority  of  these  were  found  to  furnish  14  to  20 
milligrams  of  iron  per  man  per  day.  Apparently  therefore 
the  typical  American  dietary  does  not  contain  any  such  sur- 
plus of  iron  as  would  justify  the  practice  of  leaving  the  supply 
of  this  element  entirely  to  chance.  The  available  data  rather 
indicate  that  foods  should  be  selected  with  some  reference  to 
the  kinds  and  amounts  of  iron  compounds  which  they  contain. 

Meats.  —  In  meat  as  ordinarily  eaten  the  iron  exists  largely 
as  hemoglobin,  due  to  the  blood  contained  in  the  muscular 
tissue  as  usually  sold  and  prepared  for  the  table.  Muscular 
tissue  washed  free  from  blood  contains  iron,  but  the  amount 
is  comparatively  small.  Since  fatty  tissue  contains  much  less 
iron,  the  iron  content  of  fat  meat  is  much  lower  than  that  of 
lean,  and  in  order  to  establish  any  useful  estimate  of  the  amount 
of  iron  in  meat  it  is  practically  necessary  to  consider  the  lean 
tissue  alone  or  to  refer  the  iron  to  the  protein  content  rather 
than  to  the  gross  weight  of  the  meat.  When  expressed  on  the 
former  basis,  the  results  will  still  be  influenced  by  the  extent  to 
which  the  blood  has  been  either  accidentally  or  intentionally 
removed  from  the  muscle. 

For  fresh  lean  beef  containing  the  full  proportion  of  blood, 
the  results  obtained  by  most  investigators  are  in  satisfactory 
agreement,  and  the  average  figure,  0.00375  P^r  cent  iron  in 
the  fresh  meat  free  from  visible  fat,  can  be  accepted  with 
Httle  danger  of  serious  error.  This  corresponds  to  about  15 
to  16  milligrams  of  iron  per  100  grams  of  protein  in  beef,  and 
since  no  certain  differences  in  iron  content  in  the  flesh  of  dif- 
ferent species  have  been  shown,  it  is  assumed  for  the  present 
that  approximately  the  same  ratio  of  iron  to  protein  will  hold 
for  meats  in  general. 

The  iron  of  meat,  as  already  mentioned,  is  largely  due  to  the 
blood  retained  in  the  m.uscular  tissue.  The  nutritive  value 
of  blood  is  often  questioned.     So  far  as  the  iron  compounds 


304  CHEMISTRY   OF  FOOD  AND   NUTRITION 

of  the  blood  are  concerned,  it  seems  to  be  established  that 
hemoglobin  and  hematin  may  be  absorbed  and  assimilated 
to  some  extent,  but  probably  not  to  such  good  advantage 
as  the  iron  compounds  of  eggs,  milk,  and  vegetable  foods. 

Eggs.  —  The  edible  portion  of  hens'  eggs  has  shown  as  the 
average  of  several  analyses  0.00303  per  cent  of  iron.  Whether 
the  iron  content  of  eggs  can  be  increased  by  giving  to  poultry 
food  rich  in  iron,  is  a  disputed  question. 

There  can  be  no  doubt  regarding  the  assimilation  and  utiliza- 
tion of  the  iron  compounds  of  eggs,  since  they  serve  for  the 
production  of  all  the  iron-holding  substances  of  the  blood  and 
tissues  of  the  chick,  there  being  no  possibility  of  the  introduction 
of  iron  from  without  during  incubation. 

Milk.  —  Analyses  of  samples  of  cow's  milk  of  various  origin 
have  given  results  varying  from  0.0002  to  0.0003  P^^"  cent,  and 
averaging  0.00024  per  cent  of  iron  in  the  fresh  substance. 

It  cannot  be  doubted  that  the  iron  of  milk  is  readily  absorbed 
and  assimilated,  since  this  constitutes  the  sole  natural  source  of 
iron  for  all  young  mammals  during  a  period  of  rapid  growth. 
Moreover,  metabolism  experiments  indicate  that  the  iron  of 
milk  is  likely  to  be  utilized  to  especially  good  advantage,  perhaps 
on  account  of  its  association  with  a  high  proportion  of  calcium. 

The  question  df  the  iron  supply  of  infants  fed  upon  diluted  or 
modified  cow's  milk  may,  however,  be  considered  at  this  point. 
It  is  now  generally  recognized  that  the  best  substitute  for 
mother's  milk  is  obtained  by  diluting  whole  cow's  milk  or  top 
milk  with  a  solution  of  lactose  or  maltose.  By  varying  the 
richness  of  the  milk  or  top  milk  used  and  the  amounts  of  water 
and  sugar  added,  the  composition  of  the  modified  milk  can  be 
controlled  at  will.  In  order  to  ascertain  whether  the  iron 
compounds  of  milk  tend  to  condense  upon  the  fat  globules  or 
for  any  other  reason  are  altered  in  their  distribution  by  the 
rising  of  the  cream,  a  sample  of  milk  was  allowed  to  stand,  and 
after  the  cream  had  risen,  the  iron  and  nitrogen  contents  were 


IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION      305 

determined  separately  in  the  upper  half,  containing  all  of  the 
cream,  and  in  the  lower  half,  which  consisted  of  skimmed  milk. 
These  analyses  showed  in  the  upper  half  0.000277  per  cent  of 
iron  and  0.54  per  cent  of  nitrogen;  in  the  lower  half  0.000293 
per  cent  of  iron  and  0.59  per  cent  of  nitrogen.  It  is  evident, 
therefore,  that  the  ratio  of  iron  to  nitrogen  was  practically  the 
same  in  the  cream  as  in  the  milk.  It  is  therefore  important  to 
recognize  that  the  iron  content  of  cow's  milk  is  Httle  if  any  higher 
than  that  of  human  milk,  while  the  protein  content  is  at  least 
twice  as  high ;  that  any  m^odification  of  cow's  milk  which  reduces 
its  protein  content  will  reduce  the  iron  content  in  practically 
the  same  proportion,  and  that  an  infant  fed  upon  cow's  milk, 
modified  or  diluted  to  contain  less  than  3  per  cent  of  protein,  is 
probably  receiving  food  poorer  in  iron  than  human  milk. 
According  to  present  estimates  an  infant  fed  on  any  modification 
of  cow's  milk  must  consume  the  equivalent  of  nearly  a  quart  of 
undiluted  milk  or  cream  in  order  to  obtain  as  much  iron  as  is 
supplied  daily  in  the  milk  of  the  average  healthy  nursing  mother. 
Since  no  such  quantity  of  cow's  milk  can  safely  be  fed  in  early 
infancy,  it  is  to  be  expected  that  during  the  first  months  of  hfe 
the  artificially  fed  infant  will  use  up  the  surplus  store  of  iron 
with  which  it  was  born  more  rapidly  than  will  the  child  of  the 
same  age  which  receives  the  milk  of  a  healthy  mother. 

Grain  products.  —  Iron  in  combination  with  protein  matter 
is  found  in  considerable  quantity  in  the  cereal  grains,  but  the 
greater  part  of  it  is  in  the  germ  and  outer  layers,  and  so  is 
rejected  in  the  making  of  the  "  finer  "  mill  products,  such  as 
patent  flour,  polished  rice,  and  new-process  corn  meal.  In 
view  of  the  part  which  the  iron  of  the  germ  takes  in  the  sprouting 
of  the  seed  and  the  nutrition  of  the  young  plant,  there  is  httle 
room  for  doubt  that  it  is  of  value  also  in  the  animal  economy. 
To  test  the  value  of  the  iron  in  the  outer  layers  of  the  grain 
Bunge  *  carried  out  the  following  experiment : 

*  Zeitschrift  fiir  physiologische  Chemie,  Vol.  25,  page  36  (1898). 
X 


3o6 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


A  litter  of  eight  rats  was  divided  into  two  groups  of  four 
each,  one  group  fed  upon  bread  from  fine  flour,  the  other  upon 
bread  made  from  flour  including  the  bran.  At  the  end  of  the 
fifth,  sixth,  eighth,  and  ninth  weeks,  respectively,  one  rat  of 
each  group  was  killed,  and  the  gain  in  weight,  the  total  amount 
of  hemoglobin,  and  the  percentage  of  hemoglobin  in  the  entire 
body  were  determined.    The  average  results  were  as  follows : 


Effect  of  Feeding  Different  Kinds  of  Bread  on  Growth  and  Iron 
Content  of  Body  in  Experiments  with  Rats 


Kind  of  Ration 

Gain  in  Weight 
OF  Body 

Total 

Hemoglobin 

IN  Body 

Proportion  of 

Hemoglobin  in 

Body 

White  bread 

Bran  bread 

Grams 

4.81 
20.76 

Grams 

0.2395 
0.3492 

Per  cent 

0.613 
0.714 

Here  the  bran-fed  rats  not  only  made  a  much  greater  general 
growth,  but  developed  both  a  greater  amount  and  a  higher 
percentage  of  hemoglobin.  There  can  be  no  doubt  that  the 
iron  and  other  ash  constituents  of  the  outer  layers  of  the  wheat 
were  well  utilized  in  these  cases. 

Vegetables  and  fruits.  —  Not  many  direct  studies  upon  the 
iron  compounds  of  the  fruits  and  vegetables  have  been  made, 
but  Stoklasa  has  separated  from  onions  an  iron-protein  com- 
pound very  similar  to  the  hematogen  obtained  by  Bunge  from 
egg  yolk,  but  containing  a  considerably  higher  proportion  of 
iron.  Preparations  similar  in  properties  were  also  obtained 
from  peas  and  from  mushrooms. 

In  view  of  the  fact  that  the  herbivorous  animals,  which  are 
less  liable  to  anemia  than  the  carnivora,  obtain  their  normal 
food  iron  entirely  from  vegetable  sources  there  is  every  reason 
to  suppose  that  man  makes  good  use  of  the  iron  of  the  fruits 
and  vegetables  in  his  diet.     Moreover,  since  (ias  Herter  has 


IRON  IN  FOOD  AND  ITS  FUNCTIONS  IN  NUTRITION      307 

shown)  anemic  conditions  and  excessive  intestinal  putrefaction 
often  go  together,  the  bulkiness  and  laxative  tendency  of  fruits 
and  vegetables,  along  with  their  relatively  high  iron  content,  are 
advantageous  in  combating  the  conditions  which  give  rise  to 
excessive  putrefaction,  and  at  the  same  time  increasing  the 
supply  of  food  iron. 

Among  typical  food  materials  omitted  from  the  above 
table  because  of  containing  Httle  if  any  iron,  may  be  men- 
tioned fat  pork,  bacon,  lard  and  suet,  butter,  salad  oil,  sugars, 
starches,  and  confectionery.  All  of  these  foods  have  high  fuel 
value,  and  many  are  economical  and  highly  important  ele- 
ments in  a  normal  dietary.  Excessive  use  of  these  foods, 
however,  would  tend  to  satisfy  the  appetite  and  supply  the 
body  with  the  needed  fuel  without  furnishing  the  desirable 
amount  of  iron.  On  the  other  hand,  the  fruits  and  fresh  vege- 
tables are  often  regarded  as  of  low  nutritive  value  because  of 
their  high  water  content  and  low  proportions  of  protein  and  fat. 
But  it  is  largely  this  property  which  makes  them  especially 
important  as  sources  of  food  iron,  because  they  can  be  added 
to  the  diet  without  replacing  the  staple  foods  of  high  calorific 
and  protein  value,  and  without  making  the  total  food  consump- 
tion excessive.  Thus  the  above  table  shows  plainly  that  the 
ratio  of  iron  both  to  protein  and  to  fuel  value  is  high  in  nearly 
all  of  the  typical  fruits  and  vegetables,  so  that  in  most  cases 
it  would  be  necessary  to  increase  only  slightly  the  amount  of 
protein  and  fuel  value  derived  from  these  sources,  in  order 
to  effect  a  material  increase  in  the  iron  content  of  the  dietary. 
The  iron  content  of  eggs  is  also  high,  but  the  cost  of  these 
is  often  such  as  to  restrict  their  use  in  families  of  limited  means, 
while  present  methods  of  drying  and  preserving  tend  to  equalize 
the  cost  and  increase  the  available  variety  of  fruits  and 
vegetables  throughout  the  year.  The  ratio  of  iron  to  fuel 
value  is  also  high  in  lean  meat,  but  here,  as  has  already  been 
pointed  out,  the  iron  exists  largely  in  the  form  of  hemoglobin, 


3o8  CHEMISTRY  OF  FOOD  AND  NUTRITION 

which  appears  to  be  of  distinctly  lower  nutritive  value  than  the 
iron  compounds  of  milk,  eggs,  and  foods  of  vegetable  origin, 
Especially  in  families  where  there  are  young  children  it  woulc 
be  a  mistake  to  rely  too  largely  upon  meat  as  a  source  of  iron 
Von  Noorden,  who  is  one  of  the  strongest  advocates  of  a  libera 
use  of  meat  in  the  adult  dietary,  says  in  regard  to  the  feeding  oJ 
children : 

"  The  necessity  of  a  generous  supply  of  vegetables  and  fruits 
must  be  particularly  emphasized.  They  are  of  the  greatest  im- 
portance for  the  normal  development  of  the  body  and  of  all  its 
functions.  As  far  as  children  are  concerned,  we  believe  we  coulc 
do  better  by  following  the  dietary  of  the  most  rigid  vegetarians 
than  by  feeding  the  children  as  though  they  were  carnivora,  ac- 
cording to  the  bad  custom  which  is  still  quite  prevalent.  .  .  , 
If  we  limit  the  most  important  sources  of  iron,  —  the  vegetables 
and  the  fruits,  —  we  cause  a  certain  sluggishness  of  blood  forma- 
tion and  an  entire  lack  of  reserve  iron,  such  as  is  normally  found 
in  the  liver,  spleen,  and  bone  marrow  of  healthy,  well-nourisheC 
individuals." 

In  an  experimental  dietary  study  made  in  New  York  Citj 
it  was  found  that  a  free  use  of  vegetables,  whole  wheat  bread, 
and  the  cheaper  sorts  of  fruits,  with  milk  but  without  meat 
resulted  in  a  gain  of  30  per  cent  in  the  iron  content  of  the  diet, 
while  the  protein,  fuel  value,  and  cost  remained  practically  the 
same  as  in  the  ordinary  mixed  diet  obtained  under  the  same 
market  conditions. 

REFERENCES 

Abderhalden.     Physiological  Chemistry,   English  Edition,   Chapter   17; 

Third  German  Edition,  Chapter  35. 
BuNGE.     Physiological  and  Pathological  Chemistry,  Chapter  25. 
Gaule.     Resorption  von  Eisen  und  Synthese  von  Haemoglobin.     Zeit- 

schriftfur  Biologic,  Vol.  35,  page  377  (1897). 
Gottlieb.     Ueber  die  Ausscheidungsverhaltnisse  des  Eisens.    Zeitschrift 

fiir  physiologische  Chemie,  Vol.  15,  page  371  (1891). 


IRON   IN  FOOD  AND  ITS   FUNCTIONS  IN  NUTRITION       309 

Macallum.  On  the  Absorption  of  Iron  in  the  Animal  Body.  Journal 
of  Physiology,  Vol.  16,  page  268  (1894) ;  also  Proceedings  Royal  Society 
(London),  Vol.  50,  page  277  (1891-1892) ;  Quarterly  Journal  of  Micro- 
scopical Science  (London),  Vol.  38,  page  175  (1896). 

NoTHNAGEL.  Encyclopedia  of  Practical  Medicine.  Diseases  of  the  Blood, 
pages  17,  339  (1905). 

Sherman.  Iron  in  Food  and  its  Functions  in  Nutrition.  Bull.  185,  OflSce 
of  Experiment  Station,  U.  S.  Dept.  Agriculture  (1907). 

SociN.  In  welcher  Form  wird  das  Eisen  resorbirt  ?  Zeitschrift  fur  physiO" 
logische  Chemie,  Vol.  15,  pages  93-139  (1891). 

Tartakowsky.  Ueber  de  Resorption  und  Assimilation  des  Eisens.  Pflil- 
gers  Archiv  fiir  die  gesammte  Physiologic,  Vol.  100,  page  586;  Vol.  loi, 
page  423  (1903,  1904). 

VoN  Wendt.  Untersuchungen  ueber  den  Eiweiss  und  Salz-Stoffwechsel 
beim  Menschen.  Skandinavisches  Archiv  fiir  Physiologic,  Vol.  17,  pages 
211-289  (1905)- 

WoLTERiNG.  Ueber  die  Resorbirbarkeit  der  Eisen-salze.  Zeitschrift  fiir 
physiologische  Chemie,  Vol.  21,  page  186  (1895). 


CHAPTER  XII 

ANTISCORBUTIC     AND     ANTINEURITIC     PROPERTIES 

OF   FOOD 

Recent  investigations  have  shown  that  food  furnishing  suf- 
ficient amounts  of  proteins,  fats,  carbohydrates,  and  inorganic 
foodstuffs  may  not  always  prove  permanently  adequate.  Some 
at  least  of  the  food  materials  which  go  to  make  up  a  completely 
adequate  diet  must  have  properties  beyond  those  which  have 
been  considered  in  the  preceding  chapters.  For  the  present 
these  additional  properties  are  best  expressed  in  terms  of  their 
physiological  effects.  The  term  "  deficiency  diseases "  has 
been  introduced  as  a  designation  for  those  disorders  which 
are  thought  to  be  due  to  dietary  deficiencies  of  this  sort,  and 
the  nature  of  the  disorder  arising  from  the  use  of  any  given  diet 
serves  to  designate  the  property  which  has  to  do  with  the  cause 
or  prevention  of  the  disease.  Scurvy  and  beriberi  have  in  recent 
years  been  considered  the  t5^ical  deficiency  diseases.  In  nor- 
mal nutrition  the  occurrence  of  scurvy  is  prevented  by  the 
antiscorbutic  properties  of  the  food.  Beriberi  is  primarily  a 
disease  of  the  nerves,  a  neuritis,  and  can  be  prevented  by  the 
use  of  food  adequate  in  antineuritic  substances  or  properties. 
Similarly  some  foods  have  growth-promoting  properties  beyond 
what  can  be  accounted  for  by  the  proteins,  fats,  carbohydrates, 
and  salts  which  they  contain. 

As  our  knowledge  in  this  field  is  not  yet  sufficiently  developed 
to  permit  a  satisfactory  chemical  classification  of  the  subject 
matter,  the  antiscorbutic  and  antineuritic  properties  of  foods 
will  be  considered  in  this  chapter,  and  the  growth-promoting 

310 


PROPERTIES  OF  FOOD  311 

properties  in  the  next.  The  reader  should  keep  clearly  in  mind 
the  fact  that  these  are  matters  of  active  investigation  at  the 
present  time  so  that  even  while  this  is  being  printed,  new  re- 
sults tending  to  modify  our  views  on  these  subjects  may  appear. 
The  present  text  is  written  chiefly  in  the  light  of  such  investi- 
gations as  were  available  in  May,  191 7. 

Scurvy  and  the  Antiscorbutic  Property  of  Food 

For  centuries  scurvy  was  one  of  the  most  common  diseases 
in  Europe  and  at  times  among  people  of  European  races  in 
North  America.  It  was  most  frequent  and  most  severe  in  the 
more  northern  regions,  where  the  people  were  often  confined  to 
a  limited  and  monotonous  diet  of  bread  or  other  grain  products 
and  meat  or  fish  through  a  large  part  of  the  year.  As  a  rule 
fruits  and  vegetables  were  eaten  only  during  their  short  natural 
season. 

On  the  long  voyages  which  followed  the  discovery  of  America, 
sailors  were  often  obliged  to  subsist  for  many  months  at  a  time 
on  food  even  more  restricted  in  variety  than  that  of  the  winter 
diet  of  Europe  because  they  were  cut  off  not  only  from  supplies 
of  fresh  fruits  and  vegetables  but  also  from  fresh  meat.  Their 
food  supplies  thus  often  consisted  essentially  of  breadstuffs 
and  salted  meats.  On  such  voyages  there  were  many  ex- 
ceedingly severe  outbreaks  of  scurvy  and  it  gradually  came  to 
be  recognized  that  scurvy  might  be  expected  when  men  were 
kept  for  a  long  time  on  diets  which  lack  fresh  food. 

The  European  sailors  whose  experiences  on  their  long  voy- 
ages to  America  did  so  much  to  establish  the  relationship  be- 
tween diet  and  scurvy  and  the  fact  that  fresh  foods,  particularly 
fresh  fruits  and  vegetables,  have  antiscorbutic  properties,  were 
also  instrumental  in  bringing  about  a  great  diminution  of  the 
disease.  They  introduced  into  Europe  from  America  the  cul- 
tivation of  the  potato  and  since  that  time,  as  potato  culture 
and  the  use  of  potatoes  as  food  throughout  the  year  have 


312  CHEMISTRY  OF  FOOD  AND  NUTRITION 

become  more  common  in  Europe,  scurvy  has  become  less 
common. 

For  the  past  two  or  three  generations  serious  epidemics  of 
scurvy  among  adults  have  not  often  occurred  except  as  the 
result  of  crop  failure,  imprisonment  with  inadequate  food  sup- 
ply, or  siege. 

In  all  such  cases  of  which  we  have  accurate  accounts  the 
common  feature  appears  to  be  the  lack  of  potatoes  or  other 
fresh  vegetable  or  fruit  in  the  diet.  Scurvy  on  shipboard  is 
now  avoided  by  carrying  more  liberal  quantities  of  potatoes 
among  the  rations,  and-,  in  case  of  long  voyages,  the  juice  of 
lemons  or  limes  is  taken  specifically  for  its  antiscorbutic  prop- 
erties. 

Garrod  called  attention  to  the  fact  that  foods  shown  by  ex- 
perience to  have  good  antiscorbutic  properties  (potatoes,  lemon 
and  lime  juices,  fruits  and  vegetables  generally)  are  rich  in 
potassium;  and  suggested  that  the  cause  of  scurvy  may  be 
too  small  an  intake  of  potassium  —  particularly  of  "  acid  veg- 
etable potassium  "  convertible  into  potassium  carbonate  on 
oxidation. 

However,  the  tendency  of  scurvy  to  occur  epidemically  (as 
well  as  some  other  pathological  features)  has  also  seemed  sug- 
gestive of  a  bacterial  origin  and  Litten  after  weighing  the  evi- 
dence available  in  the  early  years  of  this  century  wrote :  * 
"  However  fascinating  the  potassium  theory  may  be,  it  is  by 
no  means  absolutely  proven,  and  it  does  not  contradict  the 
view  that  scurvy  may,  in  spite  of  this,  be  an  infectious  disease. 
Scurvy  may  perhaps  be  assumed  to  be  an  infectious  disease  of 
a  non-contagious  nature  produced  by  a  microorganism  which 
finds  in  a  body  deficient  in  potassium  a  favorable  culture  medium 
for  its  development." 

Wright,  impressed  with  the  fact  that  experience  has  shown 
scurvy  to  develop  in  cases  in  which  the  diet  contains  a  pre- 

*  Cabot's  Diseases  of  Metabolism  (translation  from  Die  Deutsche  KUnik),  p.  399- 


PROPERTIES  OF  FOOD  313 

ponderance  of  ''  acid  forming  "  foods  such  as  bread  and  meat, 
while  foods  of  high  antiscorbutic  value,  i.e.  fruits  and  vegetables, 
are  such  as  yield  alkaline  ash,  was  led  to  advocate  the  view 
(held  also  by  Gautier)  that  the  cause  of  scurvy  is  a  sort  of  acidosis 
due  to  the  constant  production  of  a  relative  excess  of  acid  in 
metabolism.  An  outbreak  of  the  disease  among  the  English 
soldiers  besieged  in  Ladysmith  during  the  Boer  War  gave  Wright 
an  opportunity  to  test  his  views  and  he  found  that  in  the  scurvy 
patients  the  "  titration  alkalinity  "  ("  alkah  reserve  ")  of  the 
blood  was  considerably  below  normal  and  that  by  feeding  sodium 
or  potassium  salts  of  organic  acids  such  as  acetate,  citrate,  or 
lactate  he  was  able  to  effect  a  rapid  improvement  both  in  the 
scurvy  symptoms  and  in  the  blood  alkalinity. 

Hoist  and  Frohlich,  studying  experimental  scurvy  in  guinea 
pigs,  find  that  some  foods  such  as  cabbage  show  a  marked  loss 
of  antiscorbutic  power  as  the  result  of  simple  heating  or  slow 
drying,  while  others  (grains)  develop  antiscorbutic  value  in 
sprouting.  In  neither  of  these  cases  is  the  relation  of  acid-form- 
ing to  base-forming  elements  altered  and  these  authors  there- 
fore consider  that  they  have  entirely  disproven  the  acidosis 
theory  of  Wright  and  that  antiscorbutic  properties  of  foods 
have  no  connection  with  their  ash  constituents  but  are  due  to 
the  presence  of  small  quantities  of  a  specific  organic  substance 
or  substances,  of  undetermined  chemical  nature,  and  (in  most 
cases  at  least)  very  readily  destroyed  by  heat. 

Guinea  pigs  fed  exclusively  on  bread  or  grain  developed 
symptoms  which  Hoist  and  Frohlich  considered  to  be  "  identical 
in  all  essentials  with  those  of  human  scurvy."  Since  one  of 
these  symptoms  is  loss  in  weight  and  since  animals  may  fail 
to  eat  enough  of  a  one-sided  diet  to  meet  the  energy  require- 
ment, special  experiments  were  made  to  estabhsh  the  distinc- 
tion between  the  effects  of  scurvy  and  those  of  starvation  or 
undernutrition.  It  was  found  that  guinea  pigs  kept  on  an  ex- 
clusive diet  of  fresh  raw  cabbage,  dandelion  greens,  or  even 


314  CHEMISTRY  OF  FOOD  AND  NUTRITION 

carrots  may  die  of  starvation;  but  they  do  not  become  scor- 
butic. Those  ikept  on  grain  alone  regularly  became  scorbutic. 
Those  fed  grain  plus  a  moderate  allowance  of  cabbage,  dande- 
lion, carrot,  potato,  or  other  fresh  vegetable  remained  normal. 
The  antiscorbutic  properties  of  other  foods  were  then  tested 
by  adding  them  to  a  bread  or  grain  diet  and  observing  whether 
the  guinea  pigs  developed  symptoms  of  scurvy  or  not. 

Raw  cabbage,  dandehon  greens,  lettuce,  endive,  sorrel, 
potatoes,  carrots,  bananas,  apples,  and  cloudberries  all  showed 
antiscorbutic  properties  —  apparently  in  var3dng  degrees. 
Apples  and  bananas  were  thought  to  be  somewhat  less  effective 
than  the  potatoes,  lettuce,  greens,  and  berries.  Cabbage  and 
dandehon  juices  seem  to  lose  their  antiscorbutic  properties  more 
rapidly  than  the  vegetables  themselves.  Fruit  juices  and  sorrel 
juice  on  the  other  hand  retain  their  efficacy  as  antiscorbutics 
remarkably  well.  Raspberry  juice  seemed  but  httle  injured 
by  heating  for  i  hour  at  ioo°  or  even  iio°.  Acidulated  cab- 
bage or  dandelion  juice  retained  its  antiscorbutic  property 
much  better  than  the  natural  juice  of  these  vegetables.  If, 
as  these  experiments  indicate,  the  antiscorbutic  property  is 
due  to  the  presence  of  some  unstable  substance,  the  latter  would 
appear  to  be  much  more  stable  in  an  acid  than  in  a  neutral  or 
alkaline  medium. 

The  effect  of  cooking  was  studied  in  the  case  of  several  dif- 
ferent foods  with  the  following  results:  Cabbage  cooked  at 
ioo°  for  J  to  I  hour  was  still  a  good  antiscorbutic.  Carrots 
cooked  at  ioo°  for  i  hour  showed  a  great  diminution  in  antiscor- 
butic power.  Cooking  for  ^  hour  at  the  same  temperature 
showed  a  less  serious  injury  to  the  antiscorbutic  property. 
Cauliflower  was  much  injured  by  cooking  for  i  hour  at  ioo°; 
when  cooked  only  |  hour  it  was  a  much  better  antiscorbutic. 
Dandelion  leaves  lost  much  of  their  antiscorbutic  property  when 
cooked  for  i  hour  at  ioo°.  Potatoes  cooked  at  ioo°  "  in  the 
usual  way  "  (|  hour)   had  excellent  antiscorbutic  properties. 


PROPERTIES  OF  FOOD  315 

Turnips  and  kohlrabi  cooked  at  100°  had  antiscorbutic  power 
similar  to  cooked  potatoes.  Cloudberries  retained  their  effi- 
ciency after  cooking  to  a  very  marked  degree.  When  cooked 
at  100°  as  usual  they  were  still  excellent  antiscorbutics  and 
were  shown  to  retain  this  property  when  kept  for  at  least  3 
months  after  cooking.  From  this  it  would  appear  that  canned 
fruit  which  has  been  sterilized  at  temperature  of  boiling  water 
and  then  kept  in  a  cool  place  ought  to  be  a  good  antiscorbutic 
even  after  many  months,  and  in  general  that  ordinary  cooking 
of  vegetables  (or  low  temperature  pasteurization  of  milk)  de- 
stroys only  a  part  of  the  antiscorbutic  substance,  and  so  the  food 
still  possesses  antiscorbutic  properties  though  not  in  as  high 
degree  as  when  raw. 

The  results  of  several  recent  investigations  are,  however, 
not  entirely  consistent  with  the  findings  of  Hoist  and  Frohlich. 

Funk,  who  had  been  a  prominent  advocate  of  the  theory  that 
scurvy  is  due  to  deficiency  of  a  specific  unidentified  substance, 
has  recently  concluded  that  the  disease  produced  in  guinea  pigs 
by  a  diet  of  oats  (Hoist  and  Frohlich's  experimental  scurvy) 
may  be  due  to  acidosis.  It  has  also  been  found  independently 
by  Jackson  and  by  McCoUum  that  guinea  pigs  are  so  suscep- 
tible to  nutritive  disorders  with  scurvy  symptoms  when  placed 
upon  experimental  diets  as  to  make  the  interpretation  of  such 
experiments  exceedingly  difficult.  Jackson  finds  in  the  scor- 
butic tissues  of  the  experimental  animals  bacteria  of  the  Dip- 
lococcus  type  which  appear  to  be  specific  to  the  scurvy  lesions 
and  pathogenic  when  inoculated  into  other  guinea  pigs.  The 
results  of  such  inoculation  depend  largely  upon  the  diet ;  guinea 
pigs  fed  on  carrots,  cabbage,  and  hay  appear  relatively  im- 
mune, while  those  fed  on  grain  or  bread  diet  are  much  more 
susceptible.  According  to  McCollum  the  physical  character 
of  the  diet  and  of  the  resultant  intestinal  residues  is  responsible 
for  guinea  pig  scurvy.  His  examinations  of  guinea  pigs  dying 
with  scurvy  symptoms  reveal  characteristically  an  abnormal 


31 6  CHEMISTRY  OF  FOOD  AND  NUTRITION 

accumulation  of  fecal  material  in  the  caecum.  McCollum 
holds  that  the  guinea  pig  will  have  scurvy  on  any  diet  which 
does  not  contain  a  succulent  vegetable  and  that  this  is  due  to 
the  anatomical  character  of  the  digestive  tract,  the  caecum 
being  relatively  large  and  dehcate  in  this  species  and  especially 
liable  to  the  accumulation  of  fecal  residues  when  the  food  is 
not  of  suitable  physical  character.  His  guinea  pigs  showing 
typical  scurvy  symptoms  recovered  after  liberal  doses  of  petro- 
leum oil.  He  therefore  holds  that  guinea  pig  scurvy,  although 
"  referable  to  faulty  diet,  "  is  not  a  deficiency  disease,  the  fault 
lying  rather  in  the  unsatisfactory  physical  character  of  the  diet 
which  leads  to  an  injurious  accumulation  of  material  in  the  cae- 
cum. The  immediate  cause  of  the  pathological  symptoms  of 
scurvy  is  not  known.  It  may  perhaps  be  due  to  absorption  of 
toxic  substances  resulting  from  bacterial  action  in  the  caecum 
or  to  invasion  of  bacteria  through  an  injured  intestinal  wall. 
In  view  of  these  results  so  recently  reported  by  McCollum  it 
becomes  extremely  difficult  to  interpret  the  work  of  Hoist  and 
Frohlich,  who  apparently  failed  to  realize  the  part  played  by 
such  digestive  disorders. 

It  also  remains  an  open  question  whether  guinea  pig  scurvy 
and  human  scurvy  are  referable  to  the  same  causes. 

Recently,  as  a  result  of  war  conditions,  there  has  been  re- 
newed interest  in  human  scurvy  and  a  tendency  toward  the 
view  that  this  may  be  a  disease  in  which  two  factors,  a  nutri- 
tional condition  and  an  infection,  may  both  be  involved. 

It  also  seems  probable  that  the  term  '^  scurvy  "  may  have 
been  applied  to  more  than  one  disease  in  man. 

Infantile  Scurvy  (Barlow's  Disease) 

An  investigation  conducted  by  the  American  Pediatric 
Society  in  1898  showed  that  infants  developing  scurvy  had  in 
nearly  all  cases  been  fed  with  heated  milk  or  with  proprietary 
foods. 


PROPERTIES  OF  FOOD  317 

Infantile  scurvy  is  usually  quickly  cured  by  feeding  either 
raw  milk,  or  milk  which  has  been  pasteurized  at  a  low  tem- 
perature supplemented  by  some  fresh  fruit  juice  (usually  orange 
juice). 

Investigations  to  determine  whether  children  are  subject  to 
scurvy  when  fed  exclusively  upon  pasteurized  milk  have  given 
conflicting  results,  probably  for  two  reasons:  (i)  pasteurization 
of  the  milk  at  different  temperatures  or  for  different  lengths  of 
time  in  different  cases,  (2)  differences  in  susceptibility  to  scurvy 
among  infants.*  Aging  of  the  milk  may  also  be  a  factor 
(Hess). 

Hess  and  Fish  report  that  they  have  had  a  considerable 
number  of  cases  of  infantile  scurvy  among  hospital  children  fed 
on  milk  pasteurized  at  145°  F.  for  30  minutes  or  165°  F.  for 
20  minutes.  Orange  juice  was  efficient  as  a  preventive  or 
cure  and  did  not  lose  its  antiscorbutic  property  when  boiled 
for  10  minutes.  It  was  found  that  the  juice  of  the  orange  peel 
could  be  substituted  for  that  of  the  orange  as  an  antiscorbutic. 
Potato  was  found  to  be  an  excellent  antiscorbutic  for  children, 
and  the  authors  propose  that  potato  water  (made  by  mixing  a 
tablespoonful  of  boiled  potato  in  a  pint  of  water)  be  used  as  a 
diluent  instead  of  the  barley  water  now  commonly  used  in 
modifying  cow's  milk  for  infants.  They  held  that  if  this  is 
done,  no  other  antiscorbutic  will  be  necessary. 

In  his  later  papers  (1915,  191 6),  Hess  reports  that  when 
milk  which  has  been  heated  for  30  minutes  at  145°  F.  is  fed  with 
sugar  and  cereal,  but  without  orange  juice  or  other  antiscorbutic 
food,  for  from  two  to  eight  months  there  is  usually  a  develop- 
ment of  mild  scorbutic  symptoms,  or  a  subacute  scurvy  such 

*  Differences  in  susceptibility  to  scurvy  are  to  be  expected  in  view  of  the  well- 
known  fact  that  when  groups  of  men,  as  sailors  and  prisoners,  are  subjected  to  the 
same  conditions  and  partake  of  the  same  rations,  some  become  scorbutic  while  others 
do  not.  Physicians  have  also  found  that  some  infants  show  signs  of  scurvy  when 
receiving  an  amount  of  antiscorbutic  food  which  is  amply  sufficient  for  most  infants 
and  recover  when  a  diet  still  richer  in  antiscorbutics  is  given. 


31 8  CHEMISTRY  OF  FOOD  AND  NUTRITION 

as  might  pass  unrecognized.  Such  cases  are  apt  to  show  some 
but  not  all  of  the  classical  symptoms  of  infantile  scurvy  and 
usually  involve  retardation  of  growth.  Under  these  conditions 
the  addition  of  an  antiscorbutic  food  such  as  orange  juice  to 
the  diet  induces  an  increased  rate  of  growth  as  well  as  relief  of 
such  other  scorbutic  symptoms  as  may  have  developed.  Even 
if,  as  some  critics  have  suggested,  the  symptoms  reported  by 
Hess  are  somewhat  different  from  those  shown  by  well-de- 
veloped and  clearly  marked  cases  of  infantile  scurvy,  the  in- 
fluence which  the  presence  or  absence  of  antiscorbutic  food  in 
the  diet  was  shown  to  exert  upon  the  nutrition  and  rate  of 
growth  of  the  infant  is  a  matter  of  considerable  interest  from 
the  standpoint  of  food  chemistry. 

More  recently  still  (191 7),  Hess  finds  that  infantile  scurvy 
is  possibly  not  a  single  disease,  and  probably  not  a  simple 
dietary  disease.  Use  of  pasteurized  milk  is  a  contributing 
cause,  but  the  aging  of  such  milk  is  quite  as  much  a  factor  as 
the  heating.  The  diet  is  held  to  be  at  fault  in  allowing  the 
intestinal  bacteria  to  elaborate  toxins,  while  antiscorbutic 
foods  improve  intestinal  conditions  and  are  also  beneficial  as 
diuretics. 

Antineuritic  Properties  of  Food 

Our  knowledge  of  the  antineuritic  properties  of  foods  has 
been  obtained  through  the  study  of  beriberi  in  man  or  of  ex- 
perimental beriberi  in  fowls  or  pigeons.  While  the  symptoms 
of  beriberi  are  variable  the  disease  is  chiefly  characterized  by 
degeneration  of  the  nerves  beginning  with  those  of  the  ex- 
tremities ("  polyneuritis,"  "  multiple  peripheral  neuritis  "). 

For  a  long  time  beriberi  was  very  common  in  the  Orient 
(Malay  States,  Siam,  parts  of  Japan  and  the  Philippines)  and 
in  recent  years  beriberi  has  also  been  found  in  Newfoundland 
and  Labrador.  Cases  are  also  occasionally  reported  from  the 
southern  and  western  parts  of  the  United  States. 


PROPERTIES  OF  FOOD  319 

Takaki,  while  Inspector  General  in  the  Japanese  Navy,  was 
much  disturbed  at  the  large  proportion  of  men  who  suffered 
from  beriberi,  and  in  1880  began  a  systematic  investigation  which 
indicated  that  the  frequency  of  the  disease  was  more  closely  con- 
nected with  the  nature  of  the  food  than  with  any  other  probable 
factor  since  climate  was  found  to  be  without  influence  and  the 
sanitary  conditions  on  the  Japanese  ships  were  as  good  as  those 
in  the  European  navies  which  were  not  troubled  with  the  disease. 

A  Japanese  naval  vessel  with  276  men  on  a  9  months'  cruise 
from  Japan  to  New  Zealand,  Valparaiso,  and  Honolulu  had  169. 
cases  with  25  deaths.  Another  vessel  with  a  similar  crew  was 
sent  by  Takaki  over  the  same  route  with  a  ration  in  which 
the  rice  was  decreased,  the  barley  increased,  and  vegetables, 
meat,  and  condensed  milk  added.  In  this  case  only  14  men 
had  beriberi  and  each  of  these  had  failed  to  eat  his  full  allow- 
ance of  the  new  foods.  As  the  result  of  this  experiment  Takaki 
secured  the  adoption  of  his  new  ration  for  the  entire  Japanese 
navy  with  the  result  that  the  number  of  cases  of  beriberi  soon 
became  practically  negligible. 

Takaki  attributed  this  to  the  fact  that  the  new  diet  was 
richer  in  protein,  having  a  ratio  of  i  part  nitrogen  to  16  parts 
carbon,  whereas  the  old  ration  had  only  i  part  nitrogen  to  28  parts 
carbon.  The  great  reduction  in  beriberi  was  undoubtedly  due 
to  the  change  of  diet,  but  not  primarily  to  the  increased  protein 
intake.  Apparently  because  the  explanation  available  at  the 
time  was  not  sufficiently  convincing,  Takaki's  great  achievement 
was  not  fully  appreciated,  and  medical  opinion  continued  for 
several  years  to  regard  beriberi  as  possibly  an  infectious  dis- 
ease. But  no  success  attended  the  attempts  to  check  the  dis- 
ease by  sanitation,  while  indications  that  the  cause  might  be 
nutritional  continued  to  be  found. 

In  1907  Braddon  published  in  his  book,  "  The  Cause  and 
Prevention  of  Beriberi,"  a  large  amount  of  evidence  connecting 
the  disease  with  the  eating  of  polished  rice. 


320  CHEMISTRY  OF  FOOD  AND  NUTRITION 

At  about  the  same  time  Fletcher,  by  experimenting  with  the 
diet  in  a  lunatic  asylum,  showed  that  when  28  oz.  of  rice  was 
fed  daily  with  only  small  amounts  of  other  food,  the  use  of 
polished  or  unpolished  rice  was  alone  sufficient  to  determine 
the  occurrence  or  non-occurrence  of  beriberi. 

During  1 907-1 908  Eraser  and  Stanton  took  300  laborers  from 
Java  into  new  and  sanitary  quarters  in  a  virgin  jungle  and 
demonstrated  in  striking  fashion  that  with  rice  as  the  main 
part  of  the  diet,  beriberi  followed  the  use  of  polished  but  not  of 
unpolished  rice.  Many  other  observations  to  the  same  effect 
were  also  published  at  about  this  time. 

In  1909,  convinced  that  beriberi  was  related  to  diet,  the 
U.  S.  Army  Medical  Commission  in  the  Philippines  initiated 
changes  in  the  rations  of  the  ''  Philippine  Scouts  "  and  in  191 1 
Chamberlain  was  able  to  announce  the  eradication  of  the  dis- 
ease from  these  troops  by  the  substitution  of  unpolished  rice 
(and  a  small  quantity  of  beans)  for  the  polished  rice  previously 
used.  Until  the  year  19 10,  the  number  of  hospital  cases  of 
beriberi  ranged  from  115  to  618  (the  force  numbering  about  5000 
men).  During  19 10  changes  in  the  dietary  were  begun  and 
that  year  the  cases  dropped  to  50.  In  191 1  there  were  3;  in 
1912,  2;  in  1913,  none;  in  1914  up  to  June  30  (date  of  latest 
available  report)  there  was  i. 

In  1 908-1 909,  when  beriberi  was  at  its  worst  among  the  Scouts, 
the  diet  consisted  essentially  of  12  oz.  of  beef,  8  oz.  of  white 
flour,  8  oz.  of  potatoes,  and  20  oz.  of  rice  (ordinarily  poHshed). 
The  change  in  the  ration,  as  finally  decided  upon  after  some 
months  of  experimentation,  consisted  in  giving,  in  place  of  the 
20  oz.  of  poHshed  rice,  16  oz.  of  unpoHshed  rice  and  1.6  oz.  of 
dried  beans.  Experiments,  made  largely  upon  fowls  as  ex- 
plained below,  have  shown  that  while  meat  has  some  effect  in 
preventing  beriberi,  an  equal  weight  of  beans,  peas,  or  peanuts 
is  much  more  efficacious. 

A  further  improvement  could  have  been  made  by  substituting 


PROPERTIES  OF  FOOD  321 

some  whole  grain  product  for  the  white  flour  since  it  is  now 
known  that  a  diet  consisting  too  largely  of  white  flour  or  bread 
may  in  itself  be  a  cause  of  beriberi ;  *  but  this  appeared  un- 
necessary inasmuch  as  the  changes  already  noted  sufficed  to 
eradicate  the  disease. 

Chamberlain  states,  in  fact,  that  the  disease  had  disappeared 
as  the  result  of  adding  the  beans  to  the  ration,  before  the  sub- 
stitution of  unpolished  for  polished  rice  had  been  completed. 
He  believes  "  that  the  consumption  of  beans  to  the  daily  amount 
of  1.6  ounces  would,  unaided,  have  prevented  a  recurrence  of 
beriberi,  but  it  would  obviously  be  difficult  to  make  sure  that 
all  the  men  ate  their  share  of  this  article  over  long  periods,  and 
it  is  therefore  much  safer  that  the  largest  component  o*f  the 
diet,  the  rice,  should  be  of  the  unpolished  variety  and  by  itself 
sufficient  to  prevent  neuritis." 

Several  other  investigations  gave  similar  results.  These  re- 
peated demonstrations  of  a  close  connection  between  a  diet 
consisting  too  largely  of  polished  rice  and  the  occurrence  of 
beriberi  naturally  gave  a  great  impetus  to  experiments  de- 
signed to  find  what  constituents  of  the  rice  are  directly  con- 
cerned in  the  disease. 

Attempts  to  Isolate  an  Antineuritic  Substance 

Such  experiments  were  greatly  facilitated  by  the  fact,  dis- 
covered by  Eijkmann  in  1897,  that  fowls  develop  a  diseased 
condition  closely  resembling  beriberi  in  man,  when  they  are 
fed  exclusively  upon  poHshed  rice  for  3  or  4  weeks.  Ohler 
(1914)  finds  that  an  exclusive  diet  of  white  bread,  especially 
when  made  without  yeast,  has  the  same  effect  as  the  polished 
rice  diet.  This  experimental  beriberi  of  fowls  (or  ''  polyneuritis 
gallinarum  ")  does  not  occur  when  whole  rice  or  even  rice 
which  has  been  partially  milled  so  as  to  retain  the  inner  bran 

♦Little  (1914)-    The  prevalence  of  beriberi  in  Newfoundland  and  Labrador 
appears  to  be  due  to  a  diet  too  largely  restricted  to  white  bread. 
Y 


322  CHEMISTRY  OF  FOOD  AND  NUTRITION 

coat  (pericarp  or  "  silverskin  ")  is  fed.  It  was  soon  found  that 
rice  polishings  (bran)  when  added  to  the  poHshed  rice  diet  not 
only  protected  the  fowls  but  also  cured  those  which  had  already 
developed  the  disease.  Aqueous  and  alcoholic  extracts  of  the 
rice  poHshings  also  served  to  prevent  or  cure  the  disease.  The 
same  was  found  true  of  many  ordinary  foods  such  as  meat,  po- 
tatoes, beans,  peas,  and  peanuts,  the  legumes  being  especially 
efficient. 

Aron  working  on  Oriental  beriberi  in  the  Philippines,  and 
Schaumann  in  Europe,  centering  his  interest  more  particularly 
in  ship  beriberi,  were  both  impressed  with  the  fact  that  diets 
which  cause  beriberi  are  poor  in  phosphorus  and  that  foods  of 
goocf  curative  and  preventive  properties  are  rich  in  phosphorus. 
They  were  therefore  inclined  to  regard  beriberi  as  connected 
with  a  deficiency  of  phosphorus  in  the  diet.  Their  attempts  to 
prevent  or  cure  the  disease  by  adding  definitely  known  phos- 
phorus compounds  to  the  polished  rice  diet  gave,  however,  for 
the  most  part  negative  results.  In  Aron's  experiments  the 
deleterious  effects  seemed  to  be  reduced  though  not  excluded 
when  phytin  was  fed.  In  Schaumann's  experiments  yeast 
lecithin  and  yeast  nucleic  acid  seemed  effective,  but  egg  lecithin, 
phytin,  simple  phosphates,  and  glycerophosphate  showed  no 
beneficial  results.  The  direct  evidence  for  the  "  phosphorus 
theory  "  is  therefore  weak  and  somewhat  conflicting.  (This 
does  not  exclude  the  possibihty  that  deficiency  of  phosphatids 
may  be  at  least  a  factor  in  the  nerve  degeneration  as  argued  by 
Schaumann.) 

Furthermore,  Fraser  and  Stanton  showed  that  an  extract  of 
rice  poHshings  which  contained  only  15  per  cent  of  its  total 
phosphorus  was  capable  of  preventing  the  neuritis,  while  the 
residue  containing  the  other  85  per  cent  of  the  phosphorus  was 
ineffective;  and  soon  afterward  Chamberlain  and  Vedder 
showed  that  an  alcohohc  extract  of  rice  polishings  which  was 
highly  protective  contained  only  0.0007  per  cent  of  phosphorus 


PROPERTIES  OF  FOOD  3^3 

or  less  than  one  part  in  one  thousand  of  the  phosphorus  originally 
present  in  the  polishings. 

Chamberiain  and  his  associates  also  tried  the  effects  of 
various  inorganic  salts,  of  sugar,  phytin,  lecithin,  allantoin, 
choline,  and  many  of  the  amino  acids,  all  of  which  proved  in- 
sufficient to  prevent  the  development  of  polyneuritis  in  fowls 
kept  on  a  polished  rice  diet.  On  the  other  hand,  they  added  to 
the  knowledge  of  the  properties  of  the  antineuritic  substance 
by  a  study  of  the  effectiveness  of  rice  bran  extracts  after  dif- 
ferent treatment.  The  antineuritic  substance  was  found  to 
be  insoluble  in  ether  but  soluble  in  alcohol  or  in  water  and 
dialyzable.  It  was  not  volatile  but  was  destroyed  by  heating 
or  by  alkah ;  in  the  presence  of  acid,  it  was  more  stable.  It 
was  not  precipitated  by  lead  acetate.  They  held  the  curative 
substance  to  be  an  organic  base  but  not  an  alkaloid.  Bean 
extracts  were  found  to  contain  one  or  more  substances  having 
similar  properties.  Fresh  milk,  meat,  and  potatoes  were  also 
found  to  have  antineuritic  properties. 

Later  in  191 1  and  early  in  191 2,  several  investigators  inde- 
pendently and  almost  simultaneously  succeeded  in  isolating 
what  appeared  to  be  specific  antineuritic  substances. 

Funk's  experiments,  begun  about  the  middle  of  191 1,  have 
attracted  special  attention  since  he  was  the  first  to  announce 
(December,  191 1)  the  isolation  of  a  definite  chemical  substance 
possessing  the  antineuritic  property.  Pigeons  paralyzed  by 
neuritis  induced  by  a  pohshed  rice  diet  were  able  to  run  and 
fly  within  a  few  hours  after  administration  of  2  to  8  milligrams 
of  this  substance,  which  appeared  to  be  an  organic  nitrogenous 
base  related  to  the  pyrimidines  and  to  which  Funk  gave  the 
name  vitamine.  He  described  the  preparation  of  such  substances 
from  rice  bran  and  from  yeast,  and  inferred  the  existence  of 
the  same  or  a  similar  vitamine  in  all  foods  which  have  anti- 
neuritic properties.  Funk's  view  of  the  relation  of  vitamine  to 
the  phenomena  of  beriberi  is  as  follows :  The  lack  of  vitamine 


324  CHEMISTRY  OF  FOOD  AND  NUTRITION 

in  the  food  forces  the  animal  to  get  this  substance  from  its  own 
tissues  (with  the  result  that  there  is  wasting  of  the  muscles 
causing  emaciation  unless  accompanied  by  oedema).  After  the 
stock  of  vitamines  available  in  the  muscles  begins  to  be  scarce, 
there  results  a  breaking  down  of  the  nerve  tissue  and  the  appear- 
ance of  nervous  symptoms  such  as  are  observed  in  beriberi. 

Funk  called  this  beriberi  vilamine.  It  constituted  only  0.05  per  cent  of 
the  rice  polishings  corresponding  to  about  o.oi  per  cent  in  the  whole  grain. 

In  March,  191 2,  Edie,  Moore,  Simpson,  and  Webster  (working  independ- 
ently of  Funk)  described  the  isolation  from  yeast  of  a  base  which  promptly 
cured  pigeons  suffering  from  polyneuritis.  This  base  they  described  as 
having  composition  corresponding  to  the  formula  C7H17N2O6.  They  called 
it  toruline. 

Schaumann  (June,  191 2)  reported  the  preparation  of  a  phosphorus-free 
nitrogenous  crystallizable  base  corresponding  in  general  to  the  description 
given  by  Funk  and  exerting  a  marked  restorative  action  upon  polyneuritic 
pigeons.  This  base  he  considers  the  "activator"  in  the  cure  of  polyneuritis, 
holding  that  it  "mobilizes"  the  phosphatid  substances  which  must  be  re- 
built into  the  degenerated  nerve  tissue  in  order  to  effect  a  permanent  cure. 

In  July,  191 2,  Suzuki,  Shimamura,  and  Odake,  reported  an  extended 
investigation  of  experimental  beriberi  in  which  they  had  prepared  from  rice 
polishings  by  an  independent  method  a  base  of  high  curative  power  which 
they  called  oryzanine.  In  preparing  oryzanine  they  precipitated  an  alcoholic 
extract  of  rice  polishings  with  tannin,  decomposed  the  tannate  by  baryta, 
removed  the  barium  by  sulphuric  acid,  and  precipitated  the  base  as  a  picrate. 
Only  0.005  to  0.01  gram  of  oryzanine  was  required  to  make  the  daily  diet 
of  polished  rice  adequate  for  a  pigeon.  Since  the  pigeons  ate  25  to  30  grams 
of  rice  per  day  this  means  that  the  oryzanine  was  only  ^^^j^  to  ^^^^  of  the 
(dry)  weight  of  the  food  eaten.  Feeding  0.3  gram  cured  a  dog  that  was 
already  paralyzed  by  experimental  beriberi.* 

It  will  be  seen  that  these  independent  investigations  all  indi- 
cate that  the  antineuritic  property  shown  by  rice  poHshings, 
yeast,  and  other  natural  food  materials  is  due  to  some  basic 
nitrogenous  substance  or  substances.     Much  work  pubHshed 

*  Apropos  of  the  small  quantities  of  vitamine  or  oryzanine  necessary  for  pro- 
nounced efiEects,  Lusk  calls  attention  to  the  fact  that  epinephrine  (adrenaline),  an 
essential  of  life,  is  present  in  the  blood  to  the  extent  of  only  i  part  in  100,000,000. 

i 


PROPERTIES  OF  FOOD  325 

since  191 2  confirms  this  general  view  without  establishing  the 
chemical  identity  of  either  "  Funk's  base,"  or  "  toruline  "  or 
"  oryzanine."  Pending  chemical  identification  of  the  naturally 
occurring  antineuritic  base  or  bases  the  term  "  vitamines  "  is 
commonly  applied  to  them. 

While  the  antineuritic  property  of  such  "  vitamine  "  has  been 
demonstrated  usually  by  experiments  upon  animals,  Williams 
and  Saleeby  have  used  a  vitamine  preparation,  made  from  rice 
poHshings,  in  a  case  of  human  beriberi  with  good  results.  In 
connection  with  this  work  it  was  found  that  acid  hydrolysis 
renders  the  antineuritic  substance  of  rice  polishings  more  active, 
or  more  rapid  in  its  action.  It  is  possible  that  in  natural  food 
materials  or  simple  water  extracts  the  vitamine  may  exist, 
either  wholly  or  in  part,  in  combination.  This  would  account 
for  the  greater  activity  and  also  for  the  instabihty  of  the  free 
*'  purified  "  vitamine  as  compared  with  the  natural  form. 

Seidell  *  has  devised  a  method  for  obtaining  a  stable  prepara- 
tion of  the  antineuritic  vitamine  by  precipitating  it  with  hy- 
drous aluminum  silicate  (Lloyd's  reagent). 

While  the  general  view  has  been  that  a  given  organism  re- 
quires a  given  amount  of  vitamine  to  maintain  health  (pre- 
sumably a  larger  amount  to  effect  recovery  from  disease  in- 
duced by  a  previous  deficiency),  it  was  suggested  by  Braddon 
and  Cooper  (1914) ,  and  a  few  simultaneous  experiments  by  Funk, 
that  there  is  a  connection  between  the  metabolism  of  carbohy- 
drate and  of  vitamine,  so  that  the  amount  of  antineuritic  sub- 
stance required  by  the  organism  increases  with  the  quantity 
of  carbohydrate  metabohzed. 

It  has  also  been  suggested  that  the  neuritis  of  beriberi  is 
due  to  a  toxic  effect,  upon  the  nerves,  of  some  substance  formed 
in,  or  absorbed  into,  the  system  and  that  the  vitamine,  when 
present  in  normal  amounts,  acts  as  a  protection  or  antidote 
against  such  toxicity. 

*  Reprint  No.  325  from  the  Public  Health  Reports,  U.  S.  Public  Health  Service. 


326  CHEMISTRY  OF  FOOD  AND   NUTRITION 

This  hypothesis  is  difficult  to  test  and  does  not  seem  to  have 
been  much  studied.  Investigations  designed  to  connect  the 
physiological  property  with  some  definite  chemical  substance 
or  type  of  molecular  structure  have,  however,  been  continued 
and  are  yielding  most  interesting  results. 

Relation  of  Chemical  Structure  to  Antineuritic  Action 

Williams  has  attacked  this  problem  by  synthesizing  substances 
of  known  structure  and  testing  them  for  curative  action  upon 
polyneuritic  pigeons.  Since  such  chemical  examinations  as 
had  been  made  in  connection  with  previous  work  upon  active 
preparations  from  natural  foods  had  suggested  the  presence  of 
pyridine-like  substances  and  also  of  hydroxyl  groups  in  a 
benzene  ring,  WilHams  began  by  synthesizing  a  series  of  hy- 
droxy pyridines  and  other  pyridine  derivatives.  Of  these 
a-hydroxy  pyridine,  2-,  4-,  6-trihydroxy  and  2-,  3-,  4-trihydroxy 
pyridine  were  found  to  have  curative  power  when  tested  upon 
polyneuritic  pigeons.  "  The  first  of  the  curative  substances 
tested  was  a-hydroxy  pyridine.  Three  birds  were  treated  with 
excellent  results.  However,  three  others  later  showed  little  or 
no  improvement.  On  proceeding  with  the  series  of  poly  hydroxy 
compounds,  a  rapid  striking  cure  was  obtained  with  a  preparation 
of  2-,  4-,  6-trihydroxy  pyridine,  followed  by  several  partial  or 
complete  failures.  A  second  and  third  fresh  preparation,  how- 
ever, produced  two  and  three  rapid  cures  respectively.  .  .  . 
In  each  case  all  the  cures  obtained  were  of  those  pigeons  which 
were  first  treated  with  a  given  preparation,  while  those  treated 
with  the  same  preparation  a  few  days  or  weeks  later  invariably 
received  no  benefit.  It  was  obvious  that  the  substances  had 
changed  in  some  manner  so  as  to  lose  the  curative  power.  As 
there  was  no  evidence  of  decomposition  it  seemed  probable 
that  it  was  due  to  isomerization." 

This  suggested  to  Williams  that  an  isomerism  may  be  at  least 
partially  responsible  for  the  instabihty  of  the  natural  "  vita- 


PROPERTIES  OF   FOOD  327 

mines  "  of  foods  and  in  conjunction  with  Seidell  he  reinvesti- 
gated the  antineuritic  properties  of  yeast  extracts  from  this 
standpoint  and  obtained  results  indicating  that  the  antineuritic 
vitamine  of  yeast  is  an  isomer  of  adenine. 

Voegtlin  and  White  report  that  they  were  unable  to  confirm 
these  observations  on  attempting  to  repeat  the  work  of  Williams 
and  Seidell. 

Continuing  his  work  on  the  relation  of  chemical  structure  to 
antineuritic  activity  Williams  finds  that  j8-hydroxy  pyridine, 
nicotinic  acid,  trigoneUine,  and  betaine  are  also  capable  of  ex- 
istence in  forms  which  are  curative  in  the  sense  of  being  "  able 
promptly  to  dissipate  the  acute  symptoms  of  polyneuritis  galli- 
narum."  *'  On  the  basis  of  these  results  it  may  be  concluded 
with  reasonable  certainty  that  the  relief  of  the  paralysis  by  such 
substances  is  intimately  connected  with  a  betaine-Hke  ring." 

Williams  calls  attention  *  to  the  fact  that,  on  theoretical 

H 

(CH)3  =  N  -  CH2  -  CO  C 

"^^\0^  HC/^CH 

Betaine  Hcl     Jc 

\^  \ 
HN-0 
Probable  active  form  of  a-hydroxy 
pyridine  (Williams) 

grounds,  the  existence  of  betaine-Hke  tautomeric  modifications 
of  the  oxy-  and  amino-pyrimidines  and  purines  is  not  less 
probable  than  in  the  case  of  the  corresponding  derivatives  of 
pyridine,  and  proposes  to  search  for  active  isomers  in  the  pyri- 
midine  series. 

REFERENCES 

Baumann  and  Howard.  Mineral  Metabolism  of  Experimental  Scurvy 
of  Guinea  Pig.  American  Journal  of  the  Medical  Sciences,  Vol.  153, 
page  650  (191 7). 

Braddon.    The  Cause  and  Prevention  of  Beriberi. 

*  Proceedings  of  Ihe  Society  for  Experimental  Biology  and  Medicine,  Vol.  14,  page  25. 


328  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Braddon  and  Cooper.    The  Influence  of  Metabolic  Factors  in  Beriberi. 

Journal  of  Hygiene,  Vol.  14,  page  331  (1914). 
Chamberlain.     The  Eradication  of  Beriberi  from  the  Philippine  (Native) 

Scouts  by  means  of  a  Simple  Change  in  their  Dietary.    Philippine 

Journal  of  Science,  Vol.  63,  pages  133-146  (1911).     Also  Journal  Ameri- 
can Medical  Association,  Vol.  64,  page  1215  (191 5). 
Chamberlain  and  Vedder.     Etiology  of  Beriberi.    Philippine  Journal  of 

Science,  Vol.  6  B,  pages  251-258,  395-404;  Vol.  7  B,  pages   39-52 

(1911-1912). 
Chick  and  Hume.     Distribution  Among    Foodstuffs  of  the  Substances 

Required  for  the  Prevention  of  Beriberi  and  Scurvy.    Journal  of  the 

Royal  Army  Medical  Corps,  Vol.  29,  page  121  (1917). 
Darling.     The  Pathological  Affinities  of  Beriberi  and  Scurvy.    Journal 

of  the  American  Medical  Association,  Vol.  63,  pages  1290-1294  (1914). 
Edie,  Evans,  Moore,  Simpson,  and  Webster.    Anti-neuritic  Bases  of 

Vegetable  Origin  in  Relation  to  Beriberi.     Biochemical  Journal,  Vol. 

6,  pages  234-242  (191 2). 
Emmett  and  McKim.     The  Value  of  the  Yeast  Vitamine  Fraction  as  a 

Supplement  to  a  Rice  Diet.     Journal  of  Biological  Chemistry,  Vol.  32, 

page  409  (191 7). 
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fiir  Hygiene  und  Infectionskrankheiten,  Vol.  72,  pages  155-180  (1912). 
Funk.     Chemical  Nature  of  the  Substance  which  Cures  Polyneuritis  in 

Birds  Induced  by  a  Diet  of  Polished  Rice.    Journal  of  Physiology,  Vol. 

43,  pages  395-400,  and  Vol.  45,  page  75  (iQn,  1912). 
Funk.     Die  Vitamine  und  ihre  Bedeutung  fiir  die  Physiologie  und  Pathologic 

mit  besonderer  Beriicksichtigung  der  Avitaminoses  (Beriberi,  Skorbut, 

Pellagra,  Rachitis)  —  Weisbaden,  1914. 
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of  State  Medicine,  Vol.  20,  pages  341-368  (1913). 
Funk.     Nature  of  the  Disease  due  to  an  Exclusive  Oat  Diet  in  Guinea 

Pigs  and  Rabbits.    Journal  of  Biological  Chemistry,  Vol.  25,  page  409 

(July,  19 16). 
Funk  and  Schonborn.     Influence  of  Vitamine-free  Diet  upon  Carbohy-' 

drate  Metabolism.    Journal  of  Physiology,  Vol.  48,  pages328-33i  (1914)- 
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Harden  and  Zilva.    The  Alleged  Antineuritic  Properties  of  a-Hydroxy- 

pyridine  and  Adenine.     Biochemical  Journal,  Vol.  11,  page  172  (191 7). 
Hart  and  Lessing.     Der  Skorbut  der  Kleiner  Kinder. 
Hart,  Miller,  and  McCollum.    Further  Studies  of  the  Nutritive  De- 


PROPERTIES  OF  FOOD  329 

ficiencies  of  Wheat  and  Grain  Mixtures  and  the  Pathological  Condi- 
tions Produced  in  Swine  by  their  Use.  Journal  of  Biological  Chemistry j 
Vol.  25,  page  239  (June,  1916). 

Hess  and  Fish.  Infantile  Scurvy.  American  Journal  of  Diseases  of  Chil- 
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Hess.  Infantile  Scurvy.  Journal  of  American  Medical  Association,  Vol. 
65,  page  1003  (1915).  American  Journal  of  Diseases  of  Children^ 
November,  191 7. 

HoLST  AND  Frohlich.  Experimental  Studies  relating  to  Ship-Beriberi 
and  Scurvy.    Journal  of  Hygiene,  Vol.  7,  page  634  (1907). 

HoLST  AND  Frohlich.  Experimental  Scurvy.  Zeitschrift  fiir  Hygiene 
und  Infectionskrankheiten,  Vol.  72,  pages  1-120  (191 2). 

HoLST  AND  Frohlich.  Experimental  Scurvy,  II.  Zeitschrift  fiir  Hygiene 
und  Infectionskrankheiten,  Vol.  75,  pages  334-344  (1913). 

Jackson  et  al.  Experimental  Scurvy  in  Guinea  Pigs.  Journal  of  Infec- 
tious Diseases,  Vol.  19,  pages  478-510,  511-514  (September,  1916). 

Little.  Beriberi  caused  by  Fine  White  Flour.  Journal  of  the  American 
Medical  Association,  Yo\.  58,  page  2029;  Vol.  63,  page  1287  (1912-1914). 

LusK.     Science  of  Nutrition,  3d  edition.  Chapter  13. 

McCoLLUM.  Supplementary  Dietary  Relationships  among  our  Natural 
Foodstuffs.  Harvey  Society  Lectures,  1916-1917,  and  Journal  of  the 
American  Medical  Association,  Vol.  68,  pages  1379-1386  (1917). 

McCoLLUM  AND  KENNEDY.  The  Dietary  Factors  operating  in  the  Pro- 
duction of  Polyneuritis.  Journal  of  Biological  Chemistry,  Vol.  24, 
page  491  (1916). 

McCoLLUM  AND  PiTz.  The  Vitamine  Hypothesis  and  Deficiency  Diseases. 
A  Study  of  Experimental  Scurvy.  Journal  of  Biological  Chemistry, 
Vol.  31,  page  229  (1917). 

Ohler.  Experimental  Polyneuritis.  Eflfect  of  an  Exclusive  Diet  of  White 
Bread  on  Fowls.  Journal  of  Medical  Research,  Vol.  31,  pages  239-246 
(1914). 

Osborne  and  Mendel.  The  Role  of  Vitamines  in  the  Diet.  Journal  of 
Biological  Chemistry,  Vol.  31,  page  149  (191 7). 

Schaumann.  Preparation  and  Mode  of  Action  of  a  Substance  from  Rice 
Bran  which  counteracts  Experimental  Neuritis.  Archiv  fiir  Schifs- 
und  Tropen-Hygiene,  Vol.  16,  pages  349-361,  825-837  (1912). 

Seidell.  Vitamines  and  Nutritional  Diseases.  A  Stable  Form  of  Vitamine. 
Public  Health  Reports,  Vol.  31,  page  364  (February  18,  1916). 

Suzuki,  Shimamura,  and  Odake.  Oryzanine,  a  Component  of  Rice  Bran 
and  its  Physiological  Significance.  Biochemische  Zeitschrift,  Vol.  43, 
pages  89-153  (1912), 


330  CHEMISTRY  OF  FOOD  AND   NUTRITION 

Vedder.     Beriberi. 

Vedder.  The  Relation  of  Diet  to  Beriberi  and  the  Present  Status  of  Our 
Knowledge  of  the  Vitamines.  Journal  of  the  American  Medical  As- 
sociation, Vol.  67,  page  1494  (November  18,  1916). 

VoEGTLiN.  The  Importance  of  Vitamines  in  Relation  to  Nutrition  in  Health 
and  Disease.  Journal  of  the  Washington  Academy  of  Sciences,  Vol.  6, 
page  575  (1916). 

VoEGTLiN  AND  White.  Can  Adenine  Acquire  Antineuritic  Properties? 
Journal  of  Pharmacology  and  Experimental  Therapeutics,  Vol.  9,  page 
155  (December,  1916), 

Williams.     The  Chemical  Nature  of  the  "Vitamines."    Journal  of  Biologi- 
cal Chemistry,  Vol.  25,  page  437  (July,  1916) ;  Vol.  29,  page  495  (1917). 
^  Williams.    The    Chemistry   of   the   Vitamines.      Philippine   Journal   of 

Science,  Vol.  11  A,  page  49  (1916). 
^  Williams  and  Saleeby.  Experimental  Treatment  of  Human  Beriberi 
with  Constituents  of  Rice  Polishings.  Philippine  Journal  of  Science, 
Vol.  10  B,  page  99  (191 5). 
*"  Williams  and  Seidell.  The  Chemical  Nature  of  the  "Vitamines,"  II. 
Isomerism  in  Natural  Antineuritic  Substances.  Journal  of  Biological 
Chemistry,  Vol.  26,  page  431  (September,  191 6). 

YosHiKAWA,  Yana,  AND  Menals.  Studies  of  the  Blood  in  Beriberi.  Ar- 
chives of  Internal  Medicine,  Vol.  20,  page  103  (191 7). 


CHAPTER  XIII 

FOOD    IN    RELATION    TO    GROWTH    AND    DEVELOP- 
MENT    AND     THE     DIETARY     DEFICIENCIES     OF 
SOME    INDIVIDUAL    ARTICLES    OF    FOOD 

Nutritive  Requirements  of  the  Growing  Organism 

"  The  upper  limit  of  the  size  of  an  animal  is  determined  by 
heredity.  The  stature  to  which  an  animal  may  actually  attain, 
within  this  definitely  fixed  limit,  is  directly  related  to  the  way 
in  which  it  is  nourished  during  its  growing  period  "  (Waters). 

While  feeding  experiments  upon  growing  animals  and  the 
influence  of  growth  upon  food  requirements  have  been  discussed 
to  some  extent  in  previous  chapters,  the  great  importance  of 
adequate  nutrition  during  the  growing  period  demands  special 
consideration.  Recent  investigations  upon  nutrition  in  growth 
are  also  of  added  interest  in  that  the  study  of  "  growth-pro- 
moting properties  "  of  food  materials  has  broadened  our  con- 
ceptions of  food  values  and  of  nutritive  requirements  in  general. 

It  is  a  familiar  fact  that  the  growing  organism  needs  more 
energy,  protein,  and  inorganic  foodstuffs  in  proportion  to  weight 
than  does  one  which  is  full-grown.  But  even  a  Uberal  diet 
made  up  of  purified  proteins,  fats,  carbohydrates,  and  salts 
does  not  suffice  to  support  normal  growth  and  complete  de- 
velopment. 

Growth-Promoting  Substances  in  Food 

Hopkins  *  found  that  the  addition  of  very  small  amounts  of 
milk  to  diets  otherwise  composed  of  purified  foodstuffs  sufficed 

*  As  early  as  1906,  Hopkins  had  found  experimentally  and  published  in  brief 
{The  Analyst,  Vol.  31,  page  395)  the  fact  that  an  animal  cannot  live  " upon  a  mixture 

331 


332 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


to  induce  growth  in  young  rats  (Fig.  12),  and  Osborne  and 
Mendel  demonstrated  that  a  similar  growth-promoting  effect 
was  obtained  when  they  introduced  into  their  rations  of  isolated 

foodstuffs  a  moderate 
amount  of  "  protein- 
free  milk  "  —  a  powder 
made  by  removing  the 
fat,  the  casein,  and  the 
albumin  from  cow's 
milk  and  evaporating 
the  clear  filtrate  to 
dryness.  Since  in  both 
these  investigations  it 
was  found  that  milk 
ash  does  not  show  this 
property,  it  follows 
that  milk  must  contain 
some  water-soluble  or- 
ganic substance  which 
exerts  a  distinctly  fa- 
vorable effect  upon 
growth.  A  Uttle  later 
it  was  found  both  by 
McCoUum  and  Davis 
and  by  Osborne  and 
Mendel  that  the  fat 
of  milk  (butter  fat) 
also  exerts  a  growth- 
promoting  influence,  which,  as  it  is  shared  by  only  certain  other 
fats,  is  probably  not  due  to  the  glycerides  themselves,  but  rather 

of  pure  protein,  fat,  and  carbohydrate,  and  even  when  the  necessary  inorganic  mate- 
rial is  carefully  supplied  the  animal  still  cannot  flourish."  Seeking  further  light 
upon  the  chemical  nature  of  the  essential  substance  contained  in  milk  and  some 
other  natural  foods  but  not  in  the  purified  foodstuffs,  he  deferred  pubUcation  of  the 
details  of  the  experiments  until  191 2  {Journal  of  Physiology,  Vol.  44,  page  425). 


0  20  kQ, 

Fig.  12.  —  Growth  curves  of  rats.  Lower  curve 
six  rats  on  artificial  diet  alone.  Upper  curve  six 
similar  rats  receiving  in  addition  2  cc.  of  milk  each 
per  day.  Abscissae  time  in  days :  ordinates  aver- 
age weight  in  grams.  Courtesy  of  Dr.  F.  Gowland 
Hopkins. 


FOOD  IN  RELATION  TO  GROWTH  333 

to  a  fat-soluble  substance  carried  by  butter-fat  and  the  fat  of  egg 
yolk  and  in, much  smaller  quantities  if  at  aU  by  most  vegetable 
and  meat  fats.  This  fat-soluble  substance  (or  something  show- 
ing the  same  growth-promoting  property)  has  also  been  found 
by  McCoUum  to  occur  in  certain  plant  tissues  not  rich  in  fat, 
notably  in  alfalfa  and  cabbage  leaves  and  presumably  in  leaves 
generally.  Normal  growth  and  full  development,  as  shown  by 
ability  to  produce  and  nourish  healthy  young,  demands,  there- 
fore, in  addition  to  adequate  and  appropriate  suppHes  of  proteins, 
fats,  carbohydrates,  and  salts,  at  least  two  substances  or  kinds 
of  substances  which  are  distinguished  by  the  solubility  of  one 
in  water  and  of  the  other  in  fat.  These  substances,  neither  of 
which  has  yet  been  chemically  identified,  are  variously  desig- 
nated by  different  writers.  Hopkins  used  the  term  "  accessory 
factors."  Funk  calls  them  "  growth  vitamines."  McCollum 
criticizes  the  use  of  the  term  ^'  vitamine  "  and  proposes  that  until 
chemically  identified  the  substances  be  known  as  "  fat  soluble 
A  "  and  "  water  soluble  B."  The  fats  of  milk,  eggs,  and  cer- 
tain organs,  and  also  the  leaves  of  certain  plants,  are  particu- 
larly rich  in  "  fat  soluble  A  "  whereas  many  staple  foods  are 
very  poor  in  this  constituent.  "  Water  soluble  B  "  is  more 
widely  distributed,  being  found  in  the  foods  which  have  anti- 
neuritic  properties,  and  it  probably  is  the  same  as  the  sub- 
stance whose  absence  or  insufficiency  induces  polyneuritis. 

Thus  the  feeding  experiments  with  isolated  foodstuffs  have 
resulted  in  estabhshing  the  fact  (until  recently  unsuspected  and 
doubtless  responsible  for  many  of  the  failures  met  in  earher 
experiments)  that  there  are  required  for  normal  nutrition,  and 
most  conspicuously  during  growth  and  development,  these 
two  factors  A  and  B  in  addition  to  the  previously  known  fac- 
tors of  ample  energy  and  adequate  and  appropriate  supphes  of 
protein  and  of  inorganic  foodstuffs.  This  has  made  it  possible 
to  proceed  much  more  inteUigently  and  effectively  in  the  study 
of  the  relations  of  ordinary  food  materials  to  growth  and  de- 


334  CHEMISTRY  OF  FOOD  AND  NUTRITION 

velopment.  In  this  connection  it  is  important,  as  McCollum 
has  emphasized,  that  growth  and  development  be  considered 
not  only  in  terms  of  gain  in  weight  at  a  normal  rate,  but  also 
in  reference  to  the  capacity  to  produce  and  nourish  healthy 
young  at  intervals  normal  for  the  species.  A  diet  lacking  in 
growth-promoting  properties  is  apt  to  have  an  unfavorable 
eflect  upon  reproduction  and  lactation.  In  some  cases  a  de- 
ficiency may  become  manifest  in  connection  with  reproduction, 
even  when  it  has  not  appreciably  retarded  growth. 

In  a  recent  summary,*  McCollum  points  out  that  the  de- 
ficiency of  wheat  as  a  sole  food  has  been  found  to  be  associated 
with  the  nature  of  its  proteins,  of  its  ash  constituents,  its  lack 
of  the  "  fat  soluble  A,"  and  possibly  a  toxic  factor.  He  states 
that  when  wheat  and  a  good  salt  mixture  are  fed  there  is  im- 
provement in  the  condition  of  the  experimental  animals  for  a 
limited  time.  A  rat  will  grow  for  a  month  f  on  this  com- 
bination and  then  stop,  whereas  he  could  not  grow  at  all  on 
wheat  alone.  On  feeding  wheat  and  casein  only  there  is  also 
a  marked  improvement  for  a  time,  and  the  same  is  true  for  a 
mixture  of  wheat  and  butter  fat,  "  but  in  no  case  does  the 
beneficial  effect  extend  beyond  the  first  month.  These  results 
we  interpret  to  mean  that  there  were  two  at  least  of  the  dietary 
factors  involved,  unless  the  trouble  was  all  the  result  of  toxicity 
in  the  wheat  kernel.  The  next  step  was  to  feed  wheat  together 
with  two  purified  additions  as  wheat,  salts,  and  casein ;  wheat, 
salts,  and  butter  fat  .  .  .  combinations  (which)  will  make  a 
young  rat  grow  to  practically  the  normal  adult  size  and  at 
nearly  the  normal  rate,  but  rats  so  fed  will  never  produce 
young,  and  will  never  live  much  beyond  a  third  of  the  usual 
length  of  life  of  a  well-nourished  animal.     When  we  feed  wheat 

*  McCollum.  The  Present  Situation  in  Nutrition,  HoarcPs  Dairyman,  July- 
August,  1916. 

t  In  a  month  a  rat  makes  as  large  a  fraction  of  his  total  growth  as  is  made  by  a 
child  in  from  one  to  two  years. 


FOOD  IN  RELATION  TO  GROWTH  335 

with  all  three  of  the  purified  additions,  salts,  protein,  and  but- 
ter fat,  the  animals  are  perfectly  nourished  and  not  only  grow 
up  at  the  regular  rate  but  they  are  able  to  reproduce  at  fre- 
quent intervals  and  to  successfully  rear  their  young,  and  these 
young  can  complete  the  life  cycle  with  no  other  food  than  that 
on  which  their  parents  Hved." 

Thus  it  now  appears  that  the  diet  in  order  to  be  fully  and 
permanently  satisfactory  must  furnish  (i)  adequate  energy 
value,  (2)  proteins  sufficient  in  quantity  and  suitable  in  their 
amino  acid  make-up,  (3)  ash  constituents  each  in  sufficient 
quantity  and  all  in  well-balanced  proportions,  (4)  "  fat  soluble 
A,"  and  (5)  "  water  soluble  B."  All  of  these  factors  are  doubt- 
less necessary  in  order  to  make  the  diet  really  adequate  at 
any  time,  but  it  is  through  studies  of  growth  that  the  last-men- 
tioned factors  were  found,  and  all  of  the  requirements  are  plainly 
more  prominent  in  connection  with  growth,  development,  and 
reproduction  than  in  the  simple  maintenance  of  healthy  adults. 

Recognition  of  some  of  the  factors  just  mentioned  is  too  recent 
to  have  influenced  the  arrangement  of  many  of  the  feeding 
experiments  which  have  been  made  for  the  purpose  of  studying 
the  relation  of  diet  to  growth,  so  that  it  is  not  always  possible 
to  interpret  the  experimental  data  in  terms  of  these  five  cate- 
gories.   This  can,  however,  be  done  to  some  extent. 

Influence  of  Restricted  Food  Supply 

(i)  Energy 

When  a  diet  of  such  character  as  would  ordinarily  meet  all 
requirements  is  fed  to  a  growing  animal  in  amounts  too  small 
to  meet  the  growth  requirement,  it  is  plain  that  such  restriction 
may  result  in  a  deficiency  of  one,  several,  or  all  of  the  essential 
factors.  If  the  diet  is  so  selected  as  to  be  relatively  rich  in 
proteins,  ash  constituents,  and  the  factors  A  and  B,  then  re- 
striction of  the  amc^unt  of  food  will  result  primarily  in  an  energy 


336  CHEMISTRY  OF  FOOD  AND  NUTRITION 

deficit.  Waters  has  described  experiments  which  appear  to 
have  been  of  this  character.  He  reports  numerous  cases  of 
young  cattle  kept  on  restricted  amounts  of  food  of  suitable  kinds, 
the  restriction  being  such  as  to  materially  retard  the  increase 
in  weight  as  compared  with  that  of  a  full  fed  animal  of  the 
same  age,  or  even  to  hold  the  young  animal  at  stationary  weight 
at  an  age  when  it  should  have  been  growing  rapidly.  In  such 
cases  of  insufficiency  of  the  total  food  (energy)  intake  the 
skeleton  continues  to  grow,  in  height  at  least,  while  adipose 
tissue  steadily  disappears,  and  the  muscles  become  more  or  less 
depleted.  In  a  young  animal  subjected  to  this  type  of  under- 
nourishment the  skeleton  grows  in  height  to  a  much  greater 
extent  than  in  width.  Thus  in  a  full-fed  steer  the  increase  in 
length  of  foreleg  and  in  width  of  chest  were  about  equal,  while 
in  one  whose  rate  of  growth  was  retarded  by  sparse  rations  the 
width  of  chest  increased  only  one  third  as  much  as  the  length 
of  foreleg,  and  in  another  animal  of  the  same  age  whose  food 
was  so  restricted  as  to  permit  no  increase  in  weight  the  increase 
of  chest-width  was  only  one  eighth  as  much  as  the  increase  in 
foreleg.  The  ratios  actually  measured  in  typical  cases  were 
as  follows: 


Condition  of  Animal 

Width        .     Length  of 
OF  Chest     *       Foreleg 

I  —  full  fed 

I           :         0.97 

I           :         3-13 
I           :        8.00 

II  — retarded 

Ill  —  maintenance  * 

Along  with  the  narrower  skeleton  the  underfeeding  resulted  in 
muscles  of  smaller  diameter,  absence  of  subcutaneous  fat,  and 
a  general  emaciated  appearance.  Young  animals  thus  held 
at  constant  weight  when  they  should  be  growing  are  in  reahty 
undergoing  starvation.     To  quote  from  Waters'  paper : 

*  Just  enough  food  to  maintain  constant  weight  in  an  animal  which  should  have 
been  growing  rapidly  had  he  been  more  liberally  fed. 


FOOD  IN  RELATION  TO  GROWTH  337 

"  Apparently  the  animal  organism  is  capable  of  drawing  upon 
its  reserve  for  the  purpose  of  sustaining  the  growth  process  for 
a  considerable  time  and  to  a  considerable  extent.  Our  experi- 
ments indicate  that  after  the  reserve  is  drawn  upon  to  a  certain 
extent  to  support  growth,  the  process  ceases  and  there  is  no 
further  increase  in  height  or  in  length  of  bone.  From  this  point 
on,  the  animal's  chief  business  seems  to  be  to  sustain  life. 
This  law  applies  to  animals  on  a  stationary  live  weight  as  well 
as  those  being  fed  so  that  the  hve  weight  is  steadily  decHning, 
and  indeed  to  those  whose  ration,  while  above  maintenance, 
and  causing  a  gain  in  live  weight,  is  less  than  the  normal  growth 
rate  of  the  individual.  Such  an  animal  will,  while  gaining  in 
weight,  get  thinner,  because  it  is  drawing  upon  its  reserve  to 
supplement  the  ration  in  its  effort  to  grow  at  a  normal  rate." 

"  On  all  the  animals  under  observation  the  retardation  in 
height  growth  did  not  manifest  itself  at  all  until  after  the 
sparse  nourishment  had  been  continued  for  several  months. 
On  the  other  hand,  the  influence  upon  the  width  development 
was  observable  much  earher,  and  width  development  ceased 
altogether,  in  the  case  of  animals  on  a  maintenance  or  submain- 
tenance  ration,  long  before  the  height  development  had  ceased." 

"  Our  experiments  have  shown  that  within  certain  limits 
which  are  not  yet  at  all  well  defined,  retarded  growth  means 
retarded  development  of  the  organism.  Thus  an  animal  at 
twelve  months  of  age  and  weighing  on  account  of  sparse  nour- 
ishment only  400  pounds  when  it  should  under  natural  nourish- 
ment have  weighed  800  pounds,  has  not  its  tissues  as  fully 
developed  and  matured  as  they  would  have  been  had  the 
nourishment  been  normal.  For  example,  we  find  that  the  flesh 
of  steers  14-16  months  old  that  had  been  sparsely  fed  through- 
out their  lives  presented  the  general  characteristics  such  as 
color,  flavor,  etc.  of  veal  or  the  flesh  of  calf.  At  this  age  the 
flesh  of  a  highly  nourished  animal  possessed  the  characteristic 
color,  texture,  and  %vor  of  beef.     Prof.  Eckles  has  shown  that 


338  CHEMISTRY  OF  FOOD  AND  NUTRITION 

dairy  heifer  calves  heavily  fed  reach  sexual  maturity  at  from 
eight  to  ten  months  of  age,  whereas  similarly  bred  individuals 
that  were  sparsely  fed  did  not  reach  the  stage  of  puberty  under 
from  1 6  to  19  months  of  age." 

"  An  animal  which  has  been  retarded  and  which  in  its  earlier 
life  has  shown  an  asymmetric  development,  may  tend  later  to 
correct  this  asymmetry,  and  it  is  not  inconceivable  that  this 
may  be  fully  corrected  before  the  animal  has  reached  a  state  of 
complete  maturity,  or  a  point  where  growth  ceases  altogether." 

Somewhat  similar  experiments  have  been  performed  upon 
dogs  by  Aron.  Here  also  when  the  food  was  suitable  in  char- 
acter but  too  Hmited  in  amount  to  support  normal  growth  the 
young  animals  grew  in  length  and  height  but  became  thinner. 
Because  of  the  "  growth  impulse  "  such  an  underfed  young 
animal  burns  his  reserve  of  body  material  to  cover  the  deficit 
in  the  energy  intake  "  in  his  endeavor  to  grow  at  a  normal 
rate."  Such  a  condition  continued  indefinitely  results  after  a 
time  in  cessation  of  all  growth  and  finally  in  death  from  star- 
vation. A  dog  which  by  underfeeding  had  been  kept  for  a 
year  at  the  weight  which  he  had  when  5  weeks  old  and  had  be- 
come long,  tall,  and  very  thin,  and  was  then  fed  liberally  im- 
mediately gained  in  weight  and  circumference  but  appeared 
to  have  lost  the  capacity  for  further  growth  in  length  and 
height.  If,  however,  the  period  of  underfeeding  be  not  too 
prolonged,  the  animal  on  subsequently  receiving  ample  food 
may  regain  normal  proportions  and  grow  to  full  normal  size. 

Since  stationary  weight  in  the  young  animal  which  is  at- 
tempting to  grow  with  an  insufficient  energy  supply  does  not 
mean  cessation  of  all  growth  but  growth  of  bone  and  brain  at 
expense  of  adipose  tissue  and  to  some  extent  also  of  muscle, 
it  follows  that  the  body  of  such  an  animal  gradually  changes  in 
composition,  the  percentages  of  fat  and  perhaps  protein  becom- 
ing less  while  the  percentages  of  water  and  ash  increase.  If, 
however,  the  diet  is  rich  in  fat,  as  in  experiments  upon  mice 


FOOD  IN  RELATION  TO  GROWTH  339 

recently  reported  by  Mendel  and  Judson,  a  simple  diminution 
of  the  amount  of  food  to  a  point  where  gain  in  weight  ceases 
may  not  result  in  any  such  general  replacement  of  fat  by  water, 
perhaps  because  in  such  a  case  the  stunting  may  be  due  to  in- 
sufficiency of  some  of  the  other  factors  rather  than  to  an  energy 
deficit. 

The  experiments  of  Mendel  and  Judson  also  yield  interesting 
data  regarding  the  changes  which  normally  occur  in  the  water, 
fat  (ether  extract),  and  ash  content  of  the  body  during  its  most 
active  growth.  From  SS  analyses  of  the  entire  bodies  of  mice 
the  following  changes  in  composition  were  found :  (a)  increase 
insoHds  from  i6  percent  at  birth  to  a  maximum  of  35  per  cent 
at  fifty  days  with  a  subsequent  decrease  to  ^$  per  cent ;  (b)  de- 
crease in  the  proportion  of  water  in  the  fat-free  substance  from 
85.5  per  cent  at  birth  to  73  per  cent  in  the  adult  mouse ;  (c)  rapid 
increase  in  fat  from  1.85  percent  at  birth  to  about  10  percent 
followed  by  slow  increase  to  1 2  per  cent ;  (d)  increase  in  ash 
content  from  1.86  per  cent  at  birth  to  3  per  cent  in  the  adult 
mouse. 

(2)  Protein 

As  explained  in  earlier  chapters  (text  and  figures,  pages  55-68 
and  224-226),  it  was  shown  by  Osborne  and  Mendel  that  with 
a  diet  adequate  in  all  other  respects  any  one  of  a  number  of 
purified  proteins  such  as  casein,  lactalbumin,  or  edestin  might 
serve  as  the  sole  protein  both  for  maintenance  and  for  growth, 
while  gliadin  as  sole  protein  food  sufficed  for  maintenance  but 
not  for  growth,  and  zein  as  sole  protein  did  not  suffice  even  for 
maintenance.  Gliadin  contains  adequate  tryptophane  but  only 
about  I  per  cent  of  lysine ;  addition  of  lysine  to  the  gHadin 
ration  made  it  adequate  for  growth.  Zein  contains  neither 
tryptophane  nor  lysine;  addition  of  tryptophane  to  the  zein 
diet  makes  it  adequate  for  maintenance;  addition  of  both 
tryptophane  and  lysine  makes  it  adequate  for  growth. 


340  CHEMISTRY  OF  FOOD  AND   NUTRITION 

When  "  adequate  "  proteins  were  fed  in  progressively  re- 
stricted amounts,  i.e.  in  diminishing  percentage  of  the  food 
mixture,  Osborne  and  Mendel  found  that  with  different  pro- 
teins different  amino  acids  prove  to  be  the  limiting  factors  — 
e.g.  lysine  in  the  case  of  edestin,  cystine  in  the  case  of  casein. 
With  15  to  18  percent  of  casein  in  the  food  mixture  the  rate  of 
growth  was  normal ;  with  9  to  1 2  per  cent  of  casein  the  rats 
grew  more  slowly  but  normal  rate  of  growth  was  resumed  upon 
adding  3  per  cent  of  cystine  to  the  food  mixture.  With  only 
4.5-6  per  cent  of  casein  the  addition  of  the  3  per  cent  cystine 
did  not  make  the  growth  normal,  indicating  that  with  casein 
reduced  to  this  point  the  supply  of  some  other  amino  acid  had 
become  insufficient.* 

Another  case  in  which  cystine  appears  to  have  been  a  de- 
termining factor  in  tissue  growth  has  been  recorded  by  Evvard, 
Dox,  and  Guernsey  in  connection  with  their  feeding  experiments 
upon  pregnant  swine.  Here  a  difference  in  the  hair  coats  of 
the  new-born  pigs  appeared  to  be  due  to  the  different  intake  of 
cystine  in  the  food  protein  consumed  by  the  mother,  hair  being 
rich  in  sulphur,  and  cystine  the  sulphur-bearing  amino  acid  of 
the  food. 

A  so-called  incomplete  protein,  i.e.  one  which  when  fed  alone. 
is  quite  inadequate  to  meet  the  requirements  of  protein  metab- 
olism, may  nevertheless  contribute  toward  these  requirements 
to  an  important  degree  and  may  even  play  a  prominent  part 
in  promoting  growth,  as  was  strikingly  demonstrated  by  Osborne 
and  Mendel  in  experiments  in  which  they  added  zein  to  a  ration 
containing  a  small  percentage  of  lactalbumin.  (See  Fig.  4,  page 
66.)  Here  the  addition  of  zein  to  the  ration  more  than  doubled 
the  rate  of  growth.  Still  more  recently  McCoUum,  Simmonds, 
and  Pitz,  feeding  rats  on  rations  composed  of  a  single  grain 
with  supplementary  additions,  find  that  gelatin  supplements 
wheat  proteins  excellently  though  it  apparently  does  not  ap- 

*  Journal  of  Biological  Chemistry,  Vol.  20,  page  351. 


FOOD  IN  RELATION  TO  GROWTH  341 

preciably  improve  the  proteins  of  maize  or  oats.  Since  gelatinj 
although  lacking  tyrosine  and  tryptophane  is  relatively  rich  in 
lysine,  these  results  are  interpreted  as  indicating  that  lysine  is 
probably  the  hmiting  factor  in  wheat  proteins  but  not  in  the 
proteins  of  the  maize  or  of  the  oat  kernel. 

In  view  of  such  evidence  it  is  important  to  guard  against  the 
erroneous  impression  that  incomplete  proteins  are  useless  for 
growth.  The  illustrations  just  given  show  that  the  growing 
organism  may  use  such  proteins  to  extremely  good  advantage ; 
but  the  "  incomplete  "  proteins  must  not  be  permitted  to  dis- 
place the  "  complete  "  proteins  to  too  great  an  extent  if  the 
young  organism  is  to  grow  and  develop  at  a  fully  normal  rate. 

When  growth  is  retarded  by  inadequate  intake  of  protein 
or  of  a  particular  amino  acid,  the  emaciated  appearance  char- 
acteristic of  animals  attempting  to  grow  on  an  insufficient  en- 
ergy intake  is  not  to  be  expected.  Osborne  and  Mendel  have 
recorded  numerous  cases  of  suspension  of  growth  of  young 
rats,  especially  when  kept  on  rations  containing  gliadin  as  a 
sole  protein  food.  Here  the  inadequacy  of  the  lysine  intake 
results  in  retardation  or  even  complete  suspension  of  growth, 
but  the  animal  may  remain  quite  healthy  and  symmetrical. 
Moreover  rats  may  be  subjected  to  this  type  of  stunting  for  a 
remarkably  long  time  (even  as  long  as  would  normally  cover  the 
entire  growth  period)  and  still  retain  their  capacity  to  grow 
when  given  an  adequate  diet. 

In  some  cases  *  "  after  periods  of  suppression  of  growth,  even 
without  loss  of  body  weight,  growth  may  proceed  at  an  exag- 
gerated rate  for  a  considerable  period.  This  is  regarded  as 
something  apart  from  the  rapid  gains  of  weight  in  the  repair  or 
recuperation  of  tissue  actually  lost.  Despite  failure  to  grow 
for  some  time  the  average  normal  size  may  thus  be  regained  be- 
fore the  usual  period  of  growth  is  ended."     Statistical  studies 

*  Osborne,  Mendel,  Ferry,  and  Wakeman.  American  Journal  oj  Physiology,  Vol. 
40,  pages  16-20  (1916). 


342  CHEMISTRY  OF  FOOD  AND   NUTRITION 

on  children  also  indicate  that  retardation  in  early  growth  can 
usually  be  made  up  by  extra  rapid  growth  later.* 

Mendel  and  Judson  have  studied  the  influence  of  different 
types  of  protein  stunting  upon  the  composition  of  the  body  in 
the  case  of  the  mouse.  They  find  that  when  abundance  of  fat 
is  furnished  in  the  diet,  but  not  enough  protein  to  maintain 
normal  growth,  the  percentage  of  fat  in  the  animal  becomes 
greater  than  when  the  food  contains  an  adequate  amount  of 
protein  with  the  same  proportion  of  fat.  They  suggest  that: 
"  There  seems  to  be  a  tendency  to  protect  the  limited  amount 
of  protein  by  increasing  the  available  supply  of  fat  in  the  body.'* 
"  This  does  not  occur  when  growth  is  arrested  by  lack  of  lysine, 
as  in  the  use  of  gliadin  as  the  only  protein  in  the  diet,  since  in 
this  case  the  Umiting  factor  hes  not  in  the  amount  but  in  the 
nature  of  the  protein." 

(3)  Ash  Constituents 

Ash  constituents  have  long  been  recognized  as  playing  an 
important  part  in  the  growth  of  young  animals  and  of  these, 
as  we  have  already  seen,  the  elements  most  hkely  to  be  deficient 
are  calcium,  phosphorus,  and  iron.  Infants  (and  young  mam- 
mals generally)  are  born  with  a  reserve  store  of  iron  usually 
sufficient  to  supply  the  growth  requirement  up  to  about  the 
end  of  the  normal  suckling  period.  At  any  time  after  this 
initial  reserve  supply  has  been  used,  the  iron  in  the  body  will 
be  found  very  largely  localized  in  the  blood.  The  blood  con- 
stitutes less  than  7  per  cent  of  the  weight  of  the  body  but  con- 
tains more  than  70  per  cent  of  its  iron  content.  Hence  a  deficit 
of  iron  becomes  more  noticeable  in  the  blood  than  in  the  other 
tissues  —  growth  may  not  cease  but  the  child  (or  young  animal) 
may  grow  anemic ;  experiments  illustrating  this  have  been  cited 
in  the  chapter  on  iron,  and  it  has  been  shown  that  inorganic 
forms  of  iron  are  not  of  equal  nutritive  value  with  the  organic 
*  Mendel.    Biochemical  Bulletin,  Vol.  3,  page  167. 


FOOD  IN  RELATION  TO  GROWTH 


343 


forms  which  occur  naturally  in  food  materials.  To  an  even 
greater  extent  than  the  iron  is  locahzed  in  the  blood,  the  cal- 
cium of  the  body  is  locahzed  in  the  bones ;  it  is  estimated  that 
the  bones  contain  over  99  per  cent  of  the  body  calcium.  An 
inadequate  supply  of  calcium  in  the  food  during  growth  retards 
the  development  and  calcification  of  the  bones.  The  calcium 
needed  by  the  growing  organism  can  be  assimilated  from  inor- 
ganic forms.  Both  of  these 
facts  are  illustrated  by  the 
experiment  of  raising  pup- 
pies on  meat  with  and  with- 
out bones  to  gnaw  as  de- 
scribed in  Chapter  XI.  It 
has  also  been  found  that  the 
addition  of  calcium  chloride 
and  calcium  carbonate  to 
a  basal  ration  of  corn  and 
common  salt  in  the  case  of 
pregnant  swine  resulted  in 
greater  size,  more  vigor, 
bigger  bone,  and  better 
general  condition  of  the 
new-born  pigs  (Eward, 
Dox,  and  Guernsey). 

Bone  development  may 
also  be  interfered  with  by 
inadequacy  of  the  phosphorus  supply.  Several  investigators, 
in  studying  the  effect  of  diet  upon  growth  of  bone,  have  found 
that  the  bones  formed  in  a  young  animal  kept  on  phosphorus 
poor  diet  are  apt  to  be  soft,  spongy,  and  weak  (of  low  breaking 
strength) ,  and  that  this  may  be  prevented  by  the  simple  addi- 
tion of  calcium  phosphate  to  the  food. 

Since  phosphorus  is  a  prominent  constituent  not  only  of 
bones  but  of  all  the  soft  tissues  as  well,  the  effects  of  a  phos- 


Time  '">  Months 
Fig.  13.  —  Effect  upon  growth  of  adding  to 
a  diet  otherwise  adequate  a  salt  mixture  of 
such  composition  as  to  make  the  composition 
of  the  total  ash  similar  to  that  of  milk  ash ; 
immediate  resumption  after  entire  suspension 
of  growth."    Courtesy  of  Dr.  E.  V.  McCoIlum. 


344 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


phorus  deficiency  may  be  far-reaching.  In  the  experiments  of 
Hart,  McCollum,  and  Fuller,  young  pigs  on  phosphorus-poor 
food  continued  to  grow  for  some  time  but  finally  developed  not 
only  the  bone  defects  just  noted  but  also  weakness  of  the  legs, 
stupor,  and  a  more  or  less  comatose  condition  accompanied  by 
twitching  of  the  muscles,  dragging  of  the  hind  quarters,  and 


/  2  3  4 

Time  in  Months 
Fig.  14.  —  Growth  at  much  less  than  half  the  normal  rate  through  the  greater, 
part  of  the  normal  growth  period,  followed  by  accelerated  growth  upon  adding  a 
suitable  salt  mixture  to  the  diet.     Courtesy  of  Dr.  E.  V.  McCollum. 

ultimately  loss  of  weight  and  collapse.  These  effects  were  all 
prevented  by  simple  addition  of  calcium  phosphate  to  the  food. 
Hart  and  McCollum  record  cases  in  which  swine  restricted 
to  a  ration  of  corn  meal  and  corn  gluten  showed  little  or  no 
growth,  but  began  to  make  good  growth  upon  addition  to  the 
food  of  such  salts  as  to  make  the  ash  content  of  the  ration  similar 
to  that  of  milk. 


FOOD  IN  RELATION  TO  GROWTH 


345 


McCallum,  Simmonds,  and  Pitz  have  likewise  shown  that  a 
defective  inorganic  content  of  the  diet  may  also  result  in  re- 
tardation or  suspension  of  the  general  growth  of  the  young 
animal,  which  may  be  followed  by  prompt  resumption  of  growth 
(even  at  an  accelerated  rate  so  that  the  normal  weight  for  the 
age  may  be  regained)  when  a  salt  mixture  is  added  such  as  to 
make  the  total  ash  of  the  ration  similar  in  composition  to  milk 
ash  (Figs.  13  and  14). 

(4)    VlTAMINES   OR   FOOD   HORMONES 

Osborne  and  Mendel  (1913)  found  that  the  use  of  highly  puri- 
fied salts  in  rations  of  isolated  food  substances  resulted  in  less 
growth  than  when  salts  of  only  ordinary 
purity  were  fed.  This  suggested  to  them 
that  other  inorganic  salts  might  be  needed, 
and  a  ration  containing  very  small  addi- 
tions of  salts  of  iodine,  fluorine,  manganese, 
and  aluminum  was  fed  with  somewhat 
more  favorable  results  than  had  attended 
the  use  of  the  usual  (simpler)  salt  mix- 
ture; but  none  of  their  diets  composed 
entirely  of  pure  substances  gave  as  good 
results  as  the  corresponding  food  mixtures 
in  which  ^'  protein-free  milk  "  was  used, 
and  they  concluded  that  the  latter  was 
unquestionably  superior  to  any  purely  arti- 
ficial food  mixture.  This  superiority  now  g^J^^h'oraddfng  ''^flt 
seems  to  be  attributable  primarily  to  the  soluble  A "  to  a  diet  ade- 
presence  in  the  "  protein-free  milk  "  of  the  q^ate  in  all  other  respects. 
"  water  soluble  B,"  probably  identical  with  ^^^^^^  °^  ""'•  ^-  ^-  ^^- 
the  antineuritic  "  vitamine."  If  the  latter 
is  the  case,  the  substance  is  not  confined  to  milk  but  is  fairly 
widely  distributed  among  natural  food  materials.  Less  widely 
distributed  is  the  other  **  essential  accessory"  furnished  by  milk, 


Time  in  Months 


346 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


the  so-called  "  fat  soluble  A,"  to  the  presence  of  which  in  butter  * 
is  attributed  its  marked  growth-promoting  property  as  shown 
independently  by  McCollum  and  Davis  and  by  Osborne  and 
Mendel.  The  latter  find  that  in  a  diet  containing  ''protein- 
free  milk  "  and  an  adequate  protein,  5  per  cent  of  butter  fat 
usually  suffices  to  insure  normal  growth  and  in  a  few  cases  from 

I  to  3  per  cent  has  seemed 
sufficient.  When  butter 
fat  is  fractionally  crystal- 
lized from  alcohol  the 
growth-promoting  factor 
remains  in  the  oil  fraction, 
the  fractions  of  higher 
melting  point  being  in- 
effective. Lard  and  olive 
oil  were  also  found  in- 
effective, while  cod  liver 
oil  resembled  butter  fat 
in  its  growth-promoting 
property,  and  beef  fat 
shows  the  same  property 
to  a  less  degree.  Mc- 
Collum finds  the  same 
property  in  the  fat  of  egg 
yolk  and  of  animal  organs  such  as  the  kidney,  but  in  no  com- 
mercial fat  of  vegetable  origin  thus  far  examined,  although  feed- 
ing experiments  with  whole  grains  and  grain  embryos  indicate 
that  their  fats  must  carry  appreciable  amounts  of  this  growth- 
promoting  substance.  He  finds  also,  as  noted  earlier  in  the 
chapter,  that  the  same  "  fat  soluble  A  "  (as  demonstrated  by 


Z70 

J 

/ 

y^ 

/! 

/ 

•^    1,0 

i 
# 

^/ 

/ 

y 

marks  bir 
of  young 

Th 

70 

7 

/    ^ 

■thout  "Water  Soluble  B" 

30 

< 

■) 

. 

1                      A 

►              s 

Time  i"  Months 
Fig.   16.  —  Eflfect    upon    growth    of    adding 
"  water  soluble  B "  to  an  otherwise  adequate 
diet.     Courtesy  of  Dr.  E.  V.  McCollum. 


♦According  to  McCollum,  "fat  soluble  A"  is  about  30  times  more  soluble  in 
fat  than  in  water.  In  milk  about  half  of  it  is  dissolved  in  the  small  volume  of  fat 
and  about  half  in  the  large  volume  of  water  present.  Skimmed  milk  is,  therefore, 
not  wholly  devoid  of  this  substance. 


FOOD  IN  RELATION  TO  GROWTH  347 

specially  arranged  feeding  experiments)  occurs  in  relative  abun- 
dance in  alfalfa  and  cabbage  leaves  and  probably  in  green  vege- 
tables and  forage  plants  generally.  The  accompanying  charts 
(Figs.  15  and  16)  show  the  effects  of  presence  or  absence  of  A  or 
B  upon  the  growth  curves  of  young  rats.  Recognition  of  the  in- 
dependent need  for  each  of  these  substances  or  groups  of  sub- 
stances is  too  recent  for  definite  correlation  of  each  with  a  dis- 
tinct type  of  stunting.  Both  "  fat  soluble  A  "  and  "  water 
soluble  B  "  are  held  to  be  essential  for  the  maintenance  of  health 
as  well  as  for  growth.  The  fat  soluble  A  appears  to  be  dis- 
pensable, when  maintenance  alone  is  involved,  for  a  somewhat 
longer  period  than  is  the  water  soluble  B,  which  accounts  for 
the  polyneuritic  symptoms  in  birds  kept  on  polished  rice  diet 
and  the  cure  of  these  symptoms  by  the  feeding  of  extracts  of 
foods  rich  in  the  water  soluble  B.  Thus  McCoUum  and  Ken- 
nedy find  ''  that  pigeons  can  be  brought  into  the  polyneuritic 
state  by  feeding  a  diet  free  from  both  the  essential  factors  A 
and  B,  and  can  be  completely  cured  and  maintained  in  a  normal 
condition  for  at  least  35  days  on  the  same  diet  which  brought  on 
the  disease,  plus  the  water  extract  of  a  foodstuff  (rolled  oats) 
on  which  rats  cannot  grow  without  the  addition  of  butter  fat, 
but  on  which  they  do  grow  when  the  latter  is  added." 

Dietary  Deficiencies  of  Individual  Articles  of  Food 

McCoUum  and  his  associates  are  now  applying  the  above 
conceptions  to  the  study  of  the  dietary  deficiencies  of  individual 
articles  of  food.  In  a  recent  paper  *  they  present  their  plan  of 
investigation  as  follows: 

"  If  a  single  natural  food  product  fails  to  nourish  an  animal 
adequately,  it  may  be  due  to :  (a)  lack  of  sufficient  protein,  or 
to  proteins  of  poor  quality ;  (b)  an  unsatisfactory  mineral  con- 
tent due  either  to  inadequacy  of  certain  elements  in  amount,  or 

*  McCollum,  Simmonds,  and  Pitz.  Journal  of  Biological  Chemistry,  Vol.  25, 
pages  105,  132  (May,  1916). 


348  CHEMISTRY  OF  FOOD   AND  NXJTRITION 

to  unsatisfactory  proportions  among  them;  (c)  an  inadequate 
supply  of  the  fat  soluble  A ;  (d)  of  the  water  soluble  B ;  (e)  or 
some  toxic  substance  contained  therein.  One,  two,  three,  four, 
or  all  of  these  factors  may  operate  in  inducing  nutritive  dis- 
turbances. 

"  It  should  be  obvious  that  a  systematic  procedure  in  which 
we  feed  the  substance  under  investigation  supplemented  with 
(a)  pure  protein  only,  (b)  salt  mixture  additions  only,  (c)  but- 
ter fat  only,  (d)  extracts  known  to  carry  the  water  soluble  B 
and  as  little  else  as  is  possible,  will  reveal  whether  the  failure 
of  nutrition  involves  one  factor  only,  or  more  than  one.  If 
more  than  one  factor  is  involved,  a  similar  procedure,  but  with 
the  addition  of  all  possible  combinations  of  pairs  of  the  isolated 
food  ingredients  listed  above,  followed  if  need  be  by  another 
series  of  feeding  experiments  in  which  animals  are  fed  the 
natural  foodstuff  supplemented  with  three  such  uncomplicated 
additions,  in  all  possible  combinations,  and  if  necessary  another 
experiment  in  which  all  four  additions  are  made,  will  give  us 
results  which  make  it  possible  to  consider  the  components  of 
our  rations  in  an  entirely  new  light.  Provided  the  foodstuffs 
contain  a  toxic  substance,  special  procedures  will  have  to  be 
devised  for  studying  its  effects. 

"  Similar  studies  must  also  be  made  by  this  method  of  pro- 
cedure, with  pairs  of  the  important  foodstuffs  (food  materials) 
in  varying  proportions,  the  variation  of  the  mixture  including 
sufficient  range  to  reveal  the  degree  to  which  the  deficiencies 
of  the  protein  mixture  of  one  grain  are  corrected  by  the  peculiar 
quantitative  relationships  among  the  amino  acids  yielded  by 
the  proteins  of  the  other  grain.  The  same  may  be  said  for  the 
factors  other  than  protein.  In  this  way  we  shall  become  able 
to  interpret  the  biological  value  of  the  mixtures  of  natural 
foodstuffs  which  make  up  the  rations  which  are  in  common  use, 
in  which  the  attempt  is  now  made  to  make  for  safety  through 
variety.     We  have  carried  our  inquiry  into  the  nature  of  the 


FOOD  IN  RELATION  TO  GROWTH  349 

dietary  deficiencies  of  several  natural  products  far  enough  to 
convince  us  of  the  practicabiHty  of  this  method  of  study." 

Following  this  general  plan  McCollum  and  his  associates 
have  studied  the  dietary  deficiencies  of  wheat,  wheat  embryo, 
rice,  maize,  oats,  and  beans.  While  some  of  the  results  thus 
obtained  have  already  been  cited,  it  may  be  well  to  summarize 
here  the  chief  findings  with  reference  to  each  of  these  food 
materials  in  succession.  In  all  cases  the  experiments  were 
chiefly  upon  rats. 

The  wheat  kernel  when  fed  alone  did  not  induce  normal 
growth  in  the  experimental  animals.  Addition  of  either  (i) 
purified  casein,  (2)  butter  fat,  or  (3)  a  suitable  salt  mixture 
such  as  to  make  the  total  ash  of  the  ration  resemble  milk  ash  in 
composition,  was  found  to  improve  conditions  to  some  degree 
in  each  case,  but  in  no  case  did  such  a  single  addition  result  in 
normal  growth.  Neither  could  fully  satisfactory  results  be 
secured  by  the  addition  to  the  wheat  ration  of  any  two  of  these 
three  factors  mentioned ;  but  when  all  three  were  added,  the 
animals  showed  complete  growth  and  normal  reproduction. 
Hence  McCollum  concludes  that  the  wheat  kernel  is  deficient 
as  a  food  (i)  in  the  poor  quahty  of  its  protein,  (2)  in  that  it 
furnishes  an  inadequate  supply  of  "  fat  soluble  A,"  (3)  in  that 
it  has  an  unsatisfactory  inorganic  content.  He  also  believes 
that  when  the  diet  is  chiefly  made  up  of  the  entire  wheat  kernel, 
including  embryo,  the  possibility  of  a  mild  toxicity,  due  to  a 
toxic  constituent  in  the  embryo,  must  also  be  reckoned  with. 

Wheat  embryo  when  fed  alone  did  not  induce  growth  although 
it  is  rich  in  proteins  of  high  nutritive  efficiency  and  in  water 
soluble  B,  and  not  deficient  in  fat  soluble  A.  It  is  deficient  in 
its  inorganic  content;  even  so  simple  a  modification  as  the 
addition  of  2  per  cent  of  calcium  lactate  to  the  wheat  embryo 
diet  may  induce  noteworthy  growth  where  otherwise  no  growth 
takes  place.  To  an  important  extent,  according  to  these 
authors,  the  failure  gf  rats  and  swine  to  grow  on  diets  consisting 


350  CHEMISTRY  OF  FOOD  AND  NUTRITION 

largely  of  wheat  embryo  is  attributable  to  a  toxic  substance 
contained  therein,  which  appears  to  be  associated  with  the  fat. 
Extraction  of  the  fat  by  ether  removes  in  great  measure  the 
toxicity  of  the  embryo  without  necessarily  making  the  food 
deficient  in  the  fat  soluble  A.  According  to  the  authors  the 
toxicity  may  be  overcome  by  the  simple  addition  of  casein  to 
the  diet.  That  diet  may  greatly  influence  susceptibility  to 
toxicity  was  reported  by  Hunt  in  1910.  Hunt  found  great 
differences  in  susceptibility  to  acetonitrile  poisoning,  which 
differences  appeared  to  be  due  to  diet  alone.* 

Polished  rice  as  a  diet  for  growth  was  found  to  be  deficient  in 
four  respects :  (i)  its  protein  content  seemed  too  low  for  maxi- 
mum growth;  (2)  it  contained  inorganic  elements  in  insuf- 
ficient amounts  and  also  not  in  proper  proportions ;  (3)  it  was 
found  deficient  in  fat  soluble  A;   (4)  it  lacked  water  soluble  B. 

Maize  when  fed  alone  induced  no  appreciable  growth,  nor 
could  a  suitable  diet  be  made  by  mixing  the  parts  of  the  maize 
kernel  in  different  proportions.  The  proteins  of  the  maize 
kernel  contain  all  the  amino  acids  essential  for  growth,  but  it 
is  held  that  the  proportion  of  certain  of  them  is  such  that 

*  "In  extreme  cases  mice  after  having  been  fed  upon  certain  diets  may  recover 
from  forty  times  the  dose  of  acetonitrile  fatal  to  mice  kept  upon  other  diets.  It 
is,  moreover,  possible  to  alter  the  resistance  of  these  animals  at  will  and  to  overcome 
the  effects  of  one  diet  by  combining  it  with  another.  .  .  .  The  experiments  with 
oats  and  oatmeal  and  eggs  are  of  especial  interest.  In  the  earlier  parts  of  this  paper 
many  experiments  were  quoted  showing  that  a  diet  of  oatmeal  or  of  oats  usually 
leads  to  a  marked  resistance  of  mice  to  acetonitrile ;  the  experiments  quoted  in  this 
section  which  show  that  the  administration  of  certain  iodine  compounds  with  or 
subsequently  to  such  a  diet  further  increases  this  resistance,  and  the  experiments 
previously  reported  showing  that  as  far  as  the  resistance  toward  acetonitrile  is  con- 
cerned iodine  exerts  its  action  through  the  thyroid  gland,  all  point  to  the  conclusion 
that  the  resistance  caused  by  an  oat  diet  is  in  part  an  effect  exerted  upon  the  thyroid. 
This  effect  is  obtained  much  more  markedly  and  constantly  with  young,  growing 
mice.  From  these  experiments  and  considerations  it  seems  very  probable  that  it 
is  possible  to  influence,  in  a  specific  manner,  by  diet,  one  of  the  most  important 
hormones  in  the  body ;  this  is  a  comparatively  new  principle  in  dietetics  and  one 
which  may  prove  of  much  importance  "  (Hunt,  The  Efect  of  a  Restricted  Diet  and  of 
Various  Diets  upon  the  Resistance  oj  Animals  to  Certain  Poisons,  pages  56,  73). 


FOOD  IN  RELATION  TO   GROWTH  351 

when  this  is  the  sole  source  of  protein  the  growth  is  never  more 
than  about  two  thirds  normal.  The  maize  diet  always  requires 
the  addition  of  a  suitable  salt  mixture  (or  food  of  suitable  ash 
content).  Also  the  amount  of  fat  soluble  A  is  insufficient  in 
maize  to  induce  growth  at  the  normal  rate.  Normal  growth  and 
reproduction,  however,  occurred  when  maize  was  supplemented 
by  butter  fat,  purified  casein,  and  a  suitable  salt  mixture. 

The  oat  kernel,  according  to  McCoUum's  investigations,  con- 
tains protein  of  poorer  quality  than  either  the  maize  or  wheat 
kernel.  When  all  other  dietary  factors  are  properly  adjusted, 
nine  per  cent  of  oat  protein  in  the  diet  serves  to  induce  slow 
growth  for  a  time,  but  never  for  more  than  about  a  month  (ex- 
periments with  rats).  Casein,  which  serves  as  such  an  efficient 
adjunct  to  the  wheat  and  maize  proteins,  does  not  seem  to  sup- 
plement oat  protein  in  a  very  satisfactory  manner;  a  diet 
with  9  per  cent  of  protein  from  the  oat  kernel  and  10  per  cent 
pui'ified  casein  did  not  induce  growth  at  a  maximum  rate  as  did 
similar  combinations  of  casein  with  wheat  and  maize  proteins. 
In  this  connection  McCoUum  reports  the  unexpected  finding 
that  gelatin  supplements  the  protein  of  the  oat  kernel  more 
effectively  than  does  casein. 

The  ash  constituents  of  the  oat  kernel  must  always  be  sup- 
plemented in  order  to  induce  growth.  Fat  soluble  A  is  present 
in  the  oat  kernel  in  very  small  amounts.  The  amount  of  water 
soluble  B  is  adequate.  Growth  at  more  than  half  the  normal 
rate  may  be  obtained  when  the  oat  diet  is  supplemented  by  the 
addition  of  a  suitable  salt  mixture  and  either  butter  fat  or  a 
suitable  protein.  When  all  three  of  these  supplements  are 
added,  growth  is  normal  but  somewhat  slow.  McCoUum  be- 
lieves that  excessive  feeding  of  the  oat  kernel  causes  some 
injury  to  the  animal. 

The  white  bean,  when  fed  as  the  chief  component  of  the  diet, 
gave  results  indicating  that  its  proteins  are  of  lower  nutritive 
efficiency  than  thos^  of  the  cereal  grains.    The  bean  protein 


352  CHEMISTRY  OF  FOOD  AND   NUTRITION 

can  be  supplemented  by  the  addition  of  9  per  cent  of  casein  to 
the  diet.  The  inorganic  content  of  the  white  bean  is  not  such 
as  to  induce  growth,  but  must  be  supplemented  by  a  suitable 
salt  mixture  (or  by  food  of  a  different  ash  content  from  that  of 
the  bean  alone).  The  white  bean  seems  to  contain  less  of  fat 
soluble  A  than  do  the  cereal  grains.  It  contains  water  soluble 
B  in  abundance.  The  bean  diet  appeared  to  exert  an  unfa- 
vorable effect  in  that  animals  fed  on  a  diet  containing  a  smaller 
proportion  of  beans  (25  per  cent  of  the  total  food)  seemed  better 
nourished  than  those  whose  diet  contained  a  larger  proportion. 
It  is  suggested  that  beans  may  contain  some  unknown  sub- 
stance which  is  harmful  when  taken  in  too  large  an  amount; 
or  that  the  pressure  of  the  intestinal  gases  resulting  from  fer- 
mentation of  the  hemicelluloses  for  which  the  higher  animals 
have  no  digestive  enzyme  may  result  in  a  somewhat  asphyxia] 
condition  of  the  intestinal  wall,  thus  interfering  with  the  normal 
processes  of  absorption  and  unfavorably  affecting  the  general 
condition  of  nutrition. 

Seeds  in  general  are  held  by  McCollum  to  require  supplement- 
ing in  order  to  make  a  diet  which  will  support  normal  growth 
and  reproduction.  As  supplement  to  a  diet  consisting  largely 
of  the  products  of  cereal  grains  or  other  seeds,  milk  is  found  to 
be  especially  effective.  It  is  also  found  that  while  seeds  are 
not  effectively  supplemented  by  other  seeds,  they  may  be  sup- 
plemented by  the  leaves  and  probably  also  by  the  roots  and 
tubers  of  plants  so  that  it  is  feasible,  if  desired,  to  draw  a  bal- 
anced diet,  adequate  for  all  the  requirements  of  growth  and 
reproduction  in  an  omnivorous  animal,  entirely  from  the  prod- 
ucts of  plants.  Thus  McCollum  kept  rats  through  four 
generations  upon  a  carefully  adjusted  ration  of  maize,  alfalfa, 
and  cooked  peas.  Growth  and  reproduction  were  normal. 
The  mothers  successfully  suckled  young  up  to  the  normal  age 
of  weaning,  after  which  they  took  the  same  food  mixture  as  the 
adults.    In  this  connection  it  is  interesting  to  note  that  rats 


FOOD  IN  RELATION  TO  GROWTH  353 

which  were  free  to  make  their  own  selection  from  a  much 
greater  variety  of  vegetable  foods  never  grew  beyond  half  the 
normal  adult  size. 

In  practice  milk  is  found  to  be  most  highly  efficient  as  a  sup- 
plement to  diets  consisting  largely  of  seeds  or  their  products: 
"  The  dietary  should  be  built  around  bread  and  milk."  The 
chemical  constitution  of  its  proteins  and  its  high  calcium  and 
vitamine  contents  are  all  factors  in  the  unique  nutritive  efficiency 
of  milk,  and  make  it  possible  for  a  moderate  addition  of  milk 
to  render  adequate  a  diet  otherwise  composed  entirely  of  seeds. 

Cottonseed  meal  or  flour  *  constitutes  an  abundant  and  con- 
centrated source  of  protein  and  energy  which  as  yet  has  been 
but  Httle  utilized  in  human  nutrition.  This  is  doubtless  largely 
because  bad  results  have  sometimes  followed  its  use  in  stock 
feeding,  leading  to  the  general  belief  that  it  is  somewhat  toxic, 
at  least  when  used  in  considerable  quantities.  Withers  and 
Carruth  succeeded  in  extracting  from  the  kernels  of  the  cotton- 
seed a  substance,  gossypol,  which  shows  deleterious  action  when 
fed  and  to  which  the  toxicity  of  raw  cotton  seed  and  of  some 
cotton-seed  meals  was  attributed.  This  substance,  however, 
is  thermo-labile,  and  apparently  is  more  or  less  completely  de- 
stroyed by  the  heating  to  which  cotton-seed  meal  or  flour  is 
ordinarily  subjected  in  connection  with  the  processes  of  crush- 
ing and  pressing.  Feeding  experiments  to  determine  whether 
the  well-prepared  cotton-seed  meal  or  flour  now  available  for 
human  food  has  any  appreciable  toxicity,  and  to  what  extent 
it  meets  the  nutritive  requirements  of  normal  growth  and  re- 
production, have  recently  been  reported  by  Richardson  and 
Green  and  by  Osborne  and  Mendel.  Richardson  and  Green, 
feeding  a  high-grade  commercial  cotton-seed  flour,  found  that  no 
evidence  of  toxicity  appeared  although  this  flour  constituted 

*  Cotton-seed  flour  is  prepared  by  finely  grinding,  sifting,  and  perhaps  also  as- 
pirating the  meal  so  that  particles  of  lint,  hulls,  etc.,  are  removed  more  completely 
than  from  the  ordinary  cottfcn-seed  meal  used  in  stock  feeding. 
2  A 


354  CHEMISTRY  OF  FOOD  AND  NUTRITION 

45  to  50  per  cent  of  the  ration  of  albino  rats  through  four 
successive  generations  or  during  565  days  of  the  Hfe  of  an 
individual  (about  two  thirds  the  entire  normal  Hfe  span) ; 
that  the  cotton-seed  flour  met  all  protein  requirements  of  main- 
tenance and  growth,  and  when  supplemented  with  protein-free 
milk  and  butter  fat  was  able  to  support  normal  growth  and  re- 
production. They  found  that  no  better  growth  was  induced, 
but  more  frequent  reproduction  with  lower  mortality  and  more 
general  well-being  of  animals  were  obtained  when  5  per  cent  of 
casein  was  added  to  a  diet  containing  50  per  cent  cotton-seed 
flour  with  butter  fat,  protein-free  milk,  lard,  and  starch.  Nor- 
mal growth  and  reproduction  did  not  result  from  diets  con- 
taining 50  per  cent  cotton-seed  flour  in  which  there  was  a  lack 
of  butter  fat,  protein-free  milk,  or  both.  On  a  diet  containing 
fifty  per  cent  cotton-seed  flour  with  the  addition  of  casein  and 
butter  fat,  but  with  no  mineral  matter  other  than  that  from  the 
cotton  seed,  rats  grew  normally  and  reproduced,  but  the  second 
generation  did  not  make  quite  normal  growth. 

Osborne  and  Mendel  also  found  the  proteins  of  cotton-seed 
flour  to  be  efficient  in  nutrition,  not  only  when  fed  alone  in 
relatively  abundant  amounts  but  also  when  used  as  supple- 
ments to  maize  protein.  They  obtained  toxic  effects  from  the 
feeding  of  cotton-seed  kernels  but  not  from  the  cotton-seed  flour. 
Like  Withers  and  Carruth  they  demonstrated  that  the  harmful 
substance  could  be  removed  from  the  kernels  by  extraction  with 
ether ;  but  the  kernels  can  also  be  rendered  harmless  by  steam- 
ing, which  is  a  step  in  the  usual  commercial  process  of  extracting 
the  oil.  The  results  of  heating  were,  however,  not  altogether 
uniform  and  Osborne  and  Mendel  suggest  that  undue  heating 
may  render  the  meal  unpalatable  or  otherwise  unsuitable  for 
nutrition,  in  addition  to  destroying  the  original  deleterious 
substance,  and  that  these  facts  may  help  to  explain  the  con- 
flicting evidence  regarding  the  alleged  suitabiHty  of  different 
samples  of  commercial  meals. 


FOOD  IN  RELATION  TO  GROWTH  355 

These  recent  investigations  upon  cotton-seed  flour  are  worthy 
of  careful  study  both  because  of  the  great  economic  importance 
of  this  material  and  because  they  illustrate  well  the  application 
of  modern  methods  of  nutrition  research  to  the  solution  of  a 
long-standing  problem  regarding  the  utility  of  an  abundant 
but  relatively  neglected  food  material. 


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Vol.  19,  page  245  (October,  1914)- 

McCollum  and  Davis.  Influence  of  the  Plane  of  Protein  Intake  on  Growth. 
Journal  of  Biological  Chemistry,  Vol.  20,  page  415  (1915). 

McCollum  and  Davis.  Nutrition  with  Purified  Food  Substances.  Jour- 
nal  of  Biological  Chemistry,  Vol.  20,  page  641  (April,  1915). 

McCollum  and  Davis.  Influence  of  Certain  Vegetable  Fats  on  Growth. 
Journal  of  Biological  Chemistry,  Vol.  21,  page  179  (May,  191 5). 

McCollum  and  Davis.  Influence  of  Mineral  Content  of  the  Ration  on 
Growth  and  Reproduction.  Journal  of  Biological  Chemistry,  Vol.  21, 
page  615  (July,  1915). 

McCollum  and  Davis.  The  Nature  of  the  Dietary  Deficiencies  of  Rice. 
Journal  of  Biological  Chemistry,  Vol.  23,  page  181  (November,  1915). 

McCollum  and  Davis.  The  Essential  Factors  in  the  Diet  during  Growth. 
Journal  of  Biological  Chemistry,  Vol.  23,  page  231  (November,  1915). 

McCollum  and  Simmonds.  A  Biological  Analysis  of  Pellagra-Producing 
Diets.  Journal  of  Biological  Chemistry,  Vol.  31,  pages  29  and  181; 
Vol.  32,  page  347  (191 7). 

McCollum,  Simmonds,  and  Pitz.  The  Nature  of  the  Dietary  Deficiencies 
of  the  Wheat  Embryo.  Journal  of  Biological  Chemistry,  Vol.  25,  page 
105  (May,  1 9 16). 


FOOD  IN  RELATION  TO   GROWTH  357 

McCoLLUM,  SiMMONDS,  AND  PiTz.  The  Relation  of  the  Unidentified  Diet- 
ary Factors,  the  Fat-soluble  A,  and  Water-soluble  B,  of  the  Diet  to  the 
Growth-promoting  Properties  of  Milk.  Journal  of  Biological  Chemistry, 
Vol.  27,  page  33  (October,  1916). 

McCoLLUM,  SiMMONDS,  AND  PiTZ.  The  Vegetarian  Diet  in  the  Light  of 
Our  Present  Knowledge  of  Nutrition.  American  Journal  of  Physiology, 
Vol.  41,  page  333  (September,  1916).  See  also  Journal  of  Biological 
Chemistry,  Vol.  30,  page  13  (May,  1917). 

McCoLLUM,  SiMMONDS,  AND  PiTZ.  The  Distribution  in  Plants  of  the  Fat 
Soluble  A,  the  Dietary  Essential  of  Butter  Fat.  American  Journal  of 
Physiology,  Vol.  41,  page  361  (September,  1916). 

McCoLLUM,  SiMMONDS,  AND  PiTz.  Dietary  Deficiencies  of  the  Maize 
Kernel.  Journal  of  Biological  Chemistry,  Vol.  28,  page  153  (December, 
1916). 

McCoLLUM,  SiMMONDS,  AND  PiTz.  The  EfTects  of  Feeding  the  Proteins  of 
the  Wheat  Kernel  at  Different  Planes  of  Intake.  Journal  of  Biological 
Chemistry,  Vol.  28,  page  211  (December,  1916). 

McCoLLUM,  SiMMONDS,  AND  PiTz.  Is  Lysine  the  Limiting  Amino  Acid  in 
the  Proteins  of  the  Wheat,  Maize,  or  Oat  Kernel?  Journal  of  Bio- 
logical Chemistry,  Vol.  28,  page  483  (January,  191 7). 

McCoLLUM,  SiMMONDS,  AND  PiTz.  The  Nature  of  the  Dietary  Deficiencies 
of  the  Oat  Kernel.  Journal  of  Biological  Chemistry,  Vol.  29,  page  341 
(March,  19 1 7). 

McCoLLUM,  SiMMONDS,  AND  PiTz.  The  Dietary  Deficiencies  of  the  White 
Bean  {Phaseolus  vulgaris).    Ibid.,  Vol.  29,  page  521  (April,  1917). 

McCrudden.  Nutrition  and  Growth  of  Bone.  Transactions  of  the  15th 
International  Congress  of  Hygiene  and  Demography,  Washington,  191 2. 

Mendel.  Viewpoints  in  the  Study  of  Growth.  Biochemical  Bulletin, 
Vol.  3,  page  156  (January,  1914). 

Mendel.  Nutrition  and  Growth.  The  Harvey  Lectures,  Series  10, 
1914-1915. 

Mendel.  Abnormalities  of  Growth.  American  Journal  of  the  Medical 
Sciences,  Vol.  153,  page  i  (January,  1917). 

Mendel  and  Judson.  Some  Interrelations  between  Diet,  Growth,  and  the 
Chemical  Composition  of  the  Body.  Proceedings  of  the  National 
Academy  of  Sciences,  Vol.  2,  page  692  (December,  1916). 

Mendel  and  Osborne.  Growth.  Journal  of  Laboratory  and  Clinical 
Medicine,  Vol.  i,  page  211  (January,  1916). 

Osborne  and  Mendel.  Feeding  Experiments  with  Isolated  Food  Sub- 
stances. Carnegie  Institution  of  Washington,  Publication  No.  156, 
Parts  I  and  II  (i^i). 


358  CHEMISTRY  OF  FOOD  AND   NUTRITION 

Osborne  and  Mendel.  R6le  of  Gliadin  in  Nutrition.  Journal  of  Biologi- 
cal Chemistry,  Vol.  12,  pages  473-510  (1912). 

Osborne  and  Mendel.  Influence  of  Butter  Fat  on  Growth.  Journal  of 
Biological  Chemistry,  Vol.  16,  pages  423-437  (1913). 

Osborne  and  Mendel.  The  Influence  of  Cod  Liver  Oil  and  Some  Other 
Fats  on  Growth.  Journal  of  Biological  Chemistry,  Vol.  17,  page  401 
(April,  19 14). 

Osborne  and  Mendel.  Relation  of  Growth  to  the  Chemical  Constituents 
of  the  Diet.    Journal  of  Biological  Chemistry,  Vol.  15,  pages  311-326 

(1913)- 

Osborne  and  Mendel.  Amino  Acids  in  Nutrition  and  Growth.  Journal 
of  Biological  Chemistry,  Vol.  17,  pages  325-349  (19 14). 

Osborne  and  Mendel.  Nutritive  Properties  of  Proteins  of  the  Maize 
Kernel.    Journal  of  Biological  Chemistry,  Vol.  18,  pages  1-16  (1914). 

Osborne  and  Mendel.  The  Comparative  Nutritive  Value  of  Certain 
Proteins  in  Growth,  and  the  Problem  of  the  Protein  Minimum.  Jour- 
nal of  Biological  Chemistry,  Vol.  20,  page  351  (1915). 

Osborne  and  Mendel.  Resumption  of  Growth  after  Long-Continued 
Failure  to  Grow.  Journal  of  Biological  Chemistry,  Vol.  23,  page  439 
(December,  1915). 

Osborne  and  Mendel.  The  Stability  of  the  Growth-Promoting  Sub- 
stance of  Butter  Fat.  Journal  of  Biological  Chemistry,  Vol.  24,  page  37 
(January,  1916). 

Osborne  AND  Mendel.  Acceleration  of  Growth  after  Retardation.  Amer- 
ican Journal  of  Physiology,  Vol.  40,  page  16  (March,  1916), 

Osborne  and  Mendel.  The  Amino  Acid  Minimum  for  Maintenance  and 
Growth,  as  exemplified  by  further  experiments  with  lysine  and  trypto- 
phan.   Journal  of  Biological  Chemistry,  Vol.  25,  page  i  (May,  1916). 

Osborne  and  Mendel.  The  Growth  of  Rats  upon  Diets  of  Isolated  Food 
Substances.     Biochemical  Journal,  Vol.  10,  page  534  (1916). 

Osborne  and  Mendel.  The  Relative  Value  of  Certain  Proteins  and  Pro- 
tein Concentrates  as  Supplements  to  Corn  Gluten.  Journal  of  Bio- 
logical Chemistry,  Vol.  29,  page  69  (February,  191 7). 

Osborne  and  Mendel.  Nutritive  Factors  in  Animal  Tissues.  Journal 
of  Biological  Chemistry,  Vol.  32,  page  309  (1917). 

Osborne  and  Mendel.  The  Use  of  Soy  Bean  as  Food.  Journal  of  Bio- 
logical Chemistry,  Vol.  32,  page  369  (1917)- 

Osborne,  Mendel,  and  Ferry.  The  Efl^ect  of  Retardation  of  Growth 
upon  the  Breeding  Period  and  Duration  of  Life  of  Rats.  Science,  Vol. 
45,  page  294  (1917)- 

Pearl.     Effect  of  Feeding  Pituitary  Substance  and  Corpus  Luteum  on 


FOOD  IN  RELATION  TO   GROWTH  359 

Egg  Production  and  Growth.  Journal  of  Biological  Chemistry^  Vol.  24, 
page  123  (February,  1916). 

Rettger.  Influence  of  Milk  Feeding  on  Mortality  and  Growth.  Journal 
of  Experimental  Medicine,  Vol.  21,  page  365  (191 5). 

Richardson  and  Green.  Nutrition  Investigations  upon  Cotton-seed  Meal. 
Journal  of  Biological  Chemistry,  Vol.  25,  page  307  (1916) ;  Vol.  30, 
page  243;   Vol.  31,  page  379  (iQi?)- 

Robertson.  (Experimental  Studies  of  Growth  and  the  Growth-control- 
ling Substance  of  the  Pituitary  Body.)  Journal  of  Biological  Chemistry, 
Vol.  24,  pages  347,  i(>2>,  385,  397,  409;  Vol.  25,  pages  625,  647,  663; 
Vol.  27,  page  393  (1916). 

Waters.  The  Capacity  of  Animals  to  Grow  under  Adverse  Conditions. 
Proceedings  of  the  Society  for  the  Promotion  of  Agricultural  Science,  Vol. 
29,  page  3  (1908). 

Waters.  Influence  of  Nutrition  on  Animal  Form.  Proceedings  of  the  So- 
ciety for  the  Prom^otion  of  Agricultural  Science,  Vol.  30,  page  70  (19 10). 


CHAPTER  XIV 

DIETARY  STANDARDS  AND  THE  ECONOMIC  USE   OF 

FOOD 

The  General  Problem  of  a  Dietary  Standard 

It  is  sometimes  asked  whether  a  normal  appetite  does  not 
indicate,  as  well  as  can  any  dietary  standard,  the  amount  of 
food  which  is  desirable  for  an  individual  in  any  given  circum- 
stances. 

In  considering  such  a  question  we  shall  hardly  expect  the 
phrase  "  amount  of  food "  to  indicate  equally  the  energy 
value,  the  protein  content,  the  content  of  each  of  the  necessary 
chemical  elements,  and  each  of  the  unidentified  dietary  essentials 
A  and  B  (or  fat  soluble  and  water  soluble  "  vitamines  ").  Since 
different  articles  of  food  vary  greatly  in  the  relative  amounts 
of  the  various  nutrients  which  they  contain,  some  one  aspect 
of  food  value  must  be  chosen  as  a  basis  in  order  to  give  definite 
meaning  to  the  phrase  "  amount  of  food."  Inasmuch  as  the 
most  prominent  of  the  nutritive  requirements  is  the  need  for 
energy,  and  the  yielding  of  energy  is  the  one  function  in  which 
practically  all  articles  of  food  take  part,  it  is  logical  to  expect 
that  "  amount  of  food  "  will  more  nearly  express  number  of 
calories  than  any  other  one  factor  of  food  value  or  nutritive 
requirement.  Observation  confirms  this  impression  and  shows 
that  men  or  other  animals  when  eating  varied  food  under  the 
unrestricted  guidance  of  hunger  and  appetite  tend  to  take  such 
quantities   as   are   proportioned    to    the   energy   requirement 

360 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      361 

whether  or  not  this  amount  meets  also  the  requirements  as 
to  each  of  the  sixteen  chemical  elements  known  to  be  necessary 
in  nutrition. 

If  then  hunger  and  appetite  be  regarded  as  guides,  primarily, 
to  the  eating  of  the  right  amount  of  food  to  meet  the  energy 
requirement,  we  may  determine  their  adequacy  in  any  given  case 
by  the  fatness  of  the  person  concerned,  since  excess  of  fuel  food 
of  whatever  kind  can  contribute  to  the  storage  of  body  fat. 

If  from  year  to  year  the  body  keeps  in  good  condition  for 
its  work  and  maintains  a  fairly  constant  weight  which  bears 
such  a  proportion  to  the  height  as  to  show  that  a  proper  amount 
of  fat  is  being  carried,  it  is  reasonably  certain  that  the  amount 
(fuel  value)  of  food  eaten  in  the  course  of  the  year  is  substantially 
that  which  is  suited  to  the  degree  of  activity  maintained.  If, 
however,  by  following  the  appetite,  one  becomes  unduly  stout 
or  unduly  thin,  or  does  not  get  sufficient  fuel  for  the  energy 
required  for  the  day's  work,  or  is  annoyed  by  digestive  disturb- 
ances indicative  of  improper  feeding,  it  is  certain  that  the 
appetite  is  in  this  case  not  a  perfect  standard.  Still  more  often 
will  the  individual  appetite  prove  an  inadequate  guide  to  such 
a  quantitative  combination  of  the  different  types  of  food  as 
shall  lead  to  a  well-balanced  intake  of  each  of  the  many  essential 
food  constituents.  Here  the  customs  and  traditions  which 
govern  the  food  economics  of  the  household  and  which  un- 
doubtedly to  some  extent  reflect  the  accumulated  experience 
of  the  race  serve  an  extremely  important  purpose  in  checking 
the  caprices  of  the  palate  and  guiding  the  individual  into  food 
habits  which  are  more  Ukely  to  conform  to  actual  needs  than 
are  the  dictates  of  the  individual  appetite.  But  the  fullest 
appreciation  of  the  value  of  household  and  social  traditions 
in  the  formation  of  good  dietary  habits  does  not  justify  the 
conclusion  that  such  traditions  will  always  lead  to  the  best 
results,  either  physiologically  or  economically.  Even  if  these 
traditions  represented  the  experience  of  past  generations  to 


362  CHEMISTRY  OF  FOOD  AND   NUTRITION 

the  fullest  imaginable  extent,  they  could  not  be  expected  to 
guide  us  in  the  use  of  foods  which  were  not  available  to  our 
predecessors  but  have  now  within  a  generation  become  a  common 
part  of  the  dietary.  Nor  is  it  reasonable  to  suppose  that  dietary 
habits  adapted  to  people  engaged  chiefly  in  outdoor  occupations 
under  frontier  conditions  will  be  equally  suited  to  the  sedentary 
city  worker  of  to-day.  Under  modern  conditions  scientific 
dietary  standards,  based  on  a  knowledge  of  food  chemistry 
and  nutritive  requirements  such  as  the  preceding  chapters 
have  attempted  to  give,  constitute  the  most  rational  guide  to 
the  formation  of  hygienic  and  economic  habits  in  the  use  of  food. 
The  earliest  attempts  to  set  dietary  standards  in  terms  of 
nutrients  were  those  of  the  German  physiologists,  among  whom 
the  most  influential  was  Voit.  He  suggested  as  a  proper 
daily  allowance  of  foodstuffs  for  a  man  at  moderate  muscular 
work: 

Protein,  118  grams. 

Fat,  56  grams. 

Carbohydrates,  500  grams. 

This  dietary  would  have  a  fuel  value  of  approximately  3000 
Calories.  The  allowance  of  118  grams  of  protein,  which  has 
since  provoked  considerable  discussion,  is  said  to  have  been 
based  upon  the  average  protein  metabolism  of  many  laboring 
men  who  were  living  apparently  upon  unrestricted  diet,  so 
that  it  was  practically  the  result  of  dietary  study.  In  the 
division  of  the  remaining  calories  between  fat  and  carbohydrate, 
Voit  made  the  allowance  of  fat  low  and  of  carbohydrates  high 
in  order  to  cheapen  the  dietary. 

In  England,  Playfair  recommended  as  a  standard  for  a  man 
at  moderate  work : 

Protein,  119  grams. 

Fat,  51  grams. 

Carbohydrates,  531  grams. 


DIETARY  STANDARDS   AND  ECONOMIC  USE  OF  FOOD     363 

This  would  yield  3060  Calories  and  is  evidently  based  quite 
directly  upon  Voit's  recommendations. 

In  France,  Gautier  has  proposed  as  a  standard  for  men  with 
little  muscular  work : 

Protein,  107  grams. 

Fat,  65  grams. 

Carbohydrates,  407  grams. 

This  allowance  of  nutrients  —  which  is  based  in  part  upon 
carbon  and  nitrogen  balance  experiments,  in  part  upon  studies 
of  French  famihes  selected  as  typical,  and  in  part  upon  the 
statistics  of  food  consumed  in  Paris  for  a  period  of  ten  years  — 
would  supply  2630  Calories. 

In  America,  dietary  standards  have  been  discussed  chiefly  by 
Atwater,  Chittenden,  and  Langworthy.  Atwater,  in  his  later 
writings,*  ceasing  to  make  distinction  between  fats  and  carbohy- 
drates as  sources  of  energy  in  ordinary  dietaries,  but  making 
allowances  for  different  degrees  of  muscular  activity,  rec- 
ommended the  following  standards: 


Standards  for 

Protein, 
Grams 

Fuel  Value, 
Calories 

Man  at  hard  muscular  work 

Man  at  moderately  active  muscular  work 

Man  at  sedentary  or  woman  with  moder- 
ately active  work 

Man  without  muscular  exercise  or  woman 
at  light  to  moderate  work 

150 
125 

100 

90 

4150 
3400 

2700 

2450 

That  these  standards  were  not  intended  simply  as  expressions 
of  the  actual  needs  of  the  body  is  plainly  shown  by  the  allowance 
of  150  grams  of  protein  for  a  man  at  hard  work,  as  against  100 
grams  for  a  sedentary  man.  By  his  own  experiments  with  men 
at  rest  and  at  work  in  the  respiration  calorimeter  Atwater  had 

*  Farmers'  Bulletin  I|^.  142,  U.  S.  Department  of  Agriculture.  Also  Fifteenth 
Annual  Report  Agricultural  Experiment  Station,  Storrs,  Conn.,  1903. 


364 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


demonstrated  that  muscular  work  need  not  increase  protein 
metabolism,  if  a  sufficient  amount  of  fuel  be  provided  in  the 
form  of  carbohydrates  and  fats.  Hence,  when,  in  providing  for 
muscular  work,  he  proposes  to  increase  the  protein  in  practically 
the  same  ratio  as  the  calories,  the  idea  evidently  is  not  that  such 
an  increase  is  necessary,  but  simply  that  it  was  considered 
advisable  on  general  grounds  not  to  alter  very  greatly  the 
nature  of  the  diet  in  increasing  its  amount. 

Langworthy's  Compilation  of  Results  of  Dietary  Studies 


Occupation  of  Head  of  Family 


United  States : 

Man  at  very  hard  work  (average  19  studies)     . 

Farmers,  mechanics,  etc.  (average  162  studies) 

Businessmen,  students,  etc.  (average  51  studies) 

Inmates  of  institutions,  little  or  no  muscular 
work  (average  of  49  studies)        

Very  poor  people,  usually  out  of  work  (average 

of  15  studies) 

Canada:  Factory  hands  (average  13  studies) 

England:  Workingmen 

Scotland:  Workingmen 

Ireland:  Workingmen 

Germany:  Workingmen 

Professional  men 

France :  Men  at  light  work       

Japan :  Laborers 

Professional  and  business  men 

China :  Laborers 

Egypt :  Native  laborers 

Congo :  Native  laborers 


Food  per  Man* 

PER 

Day 

Protein, 

Fuel  value, 

Grams 

Calories 

177 

6000 

100 

3425 

106 

3285 

86 

2600 

69 

2100 

108 

3480 

89 

2685 

108 

3228 

98 

3107 

134 

3061 

III 

2511 

no 

2750 

118 

4415 

87 

2190 

91 

3400 

112 

2825 

108 

2812 

*  In.  calculating  these  results  it  is  assumed  that  women  consume  0.8  as  much 
food  as  men,  and  children  of  different  ages  from  0.3  to  0.8  as  much  as  the  man 
of  the  family. 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD     365 

In  explanation  of  the  liberality  of  his  standards  Atwater 
suggested  that  *'  the  standard  must  vary  not  only  with  the 
conditions  of  activity  and  environment,  but  also  with  the  nutri- 
tive plane  at  which  the  body  is  to  be  maintained.  A  man 
may  live  and  work  and  maintain  bodily  equihbrium  on  either 
a  higher  or  a  lower  nitrogen  level,  or  energy  level.  One  essential 
question  is,  What  level  is  most  advantageous?  The  answer 
to  this  must  be  sought,  not  simply  in  metabolism  experiments 
and  dietary  studies,  but  also  in  broader  observations  regarding 
bodily  and  mental  efficiency  and  general  health,  strength,  and 
welfare." 

Langworthy,  maintaining  a  similar  point  of  view,  has  collected 
the  data  of  large  numbers  of  dietaries  believed  to  be  fairly 
representative  of  the  food  habits  of  people  of  different  occupa- 
tions in  the  United  States  and  other  countries,  and  stated  them 
in  terms  of  protein  and  calories  per  man  per  day  with  the 
results  shown  on  the  preceding  page. 

Langworthy  concludes  that  the  results  obtained,  the  world 
over,  for  persons  of  moderate  activity,  "  do  not  differ  very 
markedly  from  a  general  average  of  100  grams  of  protein  and 
3000  Calories  of  energy,  and  that  it  is  fair  to  say  that,  although 
foods  may  differ  very  decidedly,  the  nutritive  value  of  the 
diet  in  different  regions  and  under  different  circumstances  is 
very  much  the  same  for  a  like  amount  of  muscular  work." 
He  also  points  out  that  in  some  cases  this  may  not  be  apparent 
until  allowance  is  made  for  differences  in  body  weight.  Thus 
he  estimates  the  average  weight  of  the  Japanese  professional 
and  business  men  at  105  pounds,  so  that  their  food  consumption 
of  87  grams  protein  and  2190  Calories  corresponds  to  105  grams 
protein  and  3120  Calories  for  a  man  of  150  pounds,  which  agrees 
well  with  the  American  average  for  similar  employment. 

As  a  standard  for  men  with  more  muscular  activity,  such 
as  mechanics  at  moderately  active  work,  Langworthy  sug- 
gests 3500  Calories *ncluding  105  grams  of  protein. 


366  CHEMISTRY  OF  FOOD  AND  NUTRITION 

Chittenden  differs  from  those  whose  standards  have  been 
quoted  in  giving  almost  no  weight  to  the  results  of  dietary- 
studies,  holding  that  these  serve  chiefly  as  a  measure  of  self- 
indulgence,  and  that  the  true  measure  of  what  the  body  will 
most  profitably  use  is  to  be  found  in  the  results  of  experi- 
ments upon  the  protein  metabolism,  such  as  have  been  de- 
scribed in  Chapter  VIII.  On  the  basis  of  these  experiments 
he  proposes  as  a  standard  allowance  for  the  man  of  70  kilograms 
body  weight,  60  grams  of  protein  and  2800  Calories  per  day. 
For  business  and  professional  men  such  as  Chittenden  evidently 
has  in  mind,  the  allowance  of  2800  Calories  is  in  substantial 
agreement  with  earlier  estimates.  Sixty  grams  of  protein  for  a 
man  of  70  kilograms  is,  however,  decidedly  lower  than  any 
standard  previously  current. 

Energy  Allowances  for  Adults 

It  has  been  shown  in  a  previous  chapter  that  different  normal 
individuals  of  similar  age  and  physique  are  substantially  aUke 
in  their  energy  requirement  when  performing  equivalent  amounts 
of  muscular  work,  and  that  it  is  primarily  the  muscular  activity, 
and  not  personal  idiosyncrasy  or  the  amount  of  food  eaten,  w^hich 
determines  the  amount  of  energy  transformed  in  the  body.  A 
dietary  standard  of  high  fuel  value,  and  designed  to  maintain 
metabolism  on  a  high  energy  level,  provides,  therefore,  primarily 
for  a  large  amount  of  muscular  work.  If  this  work  is  not 
performed  and  the  food  continues  to  be  eaten  and  digested, 
we  may  expect  to  find  a  storage  of  fuel  in  the  body  chiefly  in 
the  form  of  fat,  and  this  is  true  whether  the  surplus  food  eaten 
is  carbohydrate,  fat,  or  protein.  Thus  the  store  of  body  fat 
which  a  person  carries  is  the  most  reliable  indication  as  to 
whether  the  amount  of  food  habitually  eaten  is  or  is  not  properly 
adjusted  to  the  work  performed.  The  storage  of  fat  does, 
however,  in  itself  modify  the  food  requirement.  While  it  is 
true,  as  has  been  shown,  that,  as  between  a  lean  and  a  fat  man 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD     367 

having  the  same  weight,  the  lean  man  will  have  the  greater  food 
requirement,  yet  it  is  also  true  that  when  any  given  man  becomes 
fat,  his  increased  size  of  body  calls  for  increased  metaboHsm  of 
energy.  The  work  involved  in  walking,  for  example,  wiU 
increase  in  proportion  to  the  weight  moved  (i.e.  to  the  weight 
of  the  body  as  a  whole) ;  and  the  work  of  respiration  will  in- 
crease about  in  proportion  to  the  weight  of  that  part  of  the  body 
which  must  be  moved  with  the  expansion  and  contraction  of  the 
lungs;  while,  if  fat  is  deposited  in  such  a  way  as  to  interfere 
directly  with  the  free  play  of  the  muscles,  there  may  be  an 
actual  lowering  of  muscular  efficiency,  so  that  a  larger  expendi- 
ture of  energy  may  be  required  in  order  to  produce  a  given 
amount  of  work.  If  the  Hberal  diet  is  continued  and  the 
digestion  remains  normal,  the  storage  of  fat  will  continue  until 
it  raises  the  energy  expenditure  of  the  body  to  a  point  where  the 
food  is  no  longer  in  excess.  If  the  store  of  fat  carried  when  this 
point  is  reached  is  excessive,  the  fuel  value  has  been  too  high ; 
if  the  store  of  fat  is  not  excessive,  the  fuel  value  of  the  diet, 
although  greater  than  would  have  been  necessary  to  maintain 
the  body  at  its  former  weight,  has  not  been  too  high,  and  the 
body  has  acquired  an  asset  whose  utility  may  not  always  be 
recognized  in  health,  but  which  may  be  of  great  value  in  case 
of  accident,  iUness,  or  exposure. 

Opinions  differ  somewhat  as  to  the  desirable  degree  of  fatness 
as  indicated  by  the  relation  of  height  to  body  weight. 

Hill  *  estimates  the  average  height  at  25  years  of  age  as 
5  feet  3  inches  for  women  and  5  feet  8  inches  for  men,  and  the 
corresponding  average  weights  as  119  and  150  pounds  respec- 
tively. He  considers  that  variations  of  10  to  15  per  cent  above 
or  below  the  average  should  be  considered  normal.  According 
to  this  estimate  the  woman  of  5  feet  3  inches  should  weigh 
not  less  than  102-107,  nor  more  than  131-136  pounds,  and  the 
man  of  5  feet  8  incjjes  not  less  than  128-135,  nor  more  than 

*  Recent  Advances  in  Physiology  and  Biochemistry. 


368 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


165-173  pounds.  These  figures  are  exclusive  of  clothing.  Hill 
considers  as  "  fat  "  those  persons  whose  weight  exceeds  the 
average  by  15  to  30  per  cent,  and  as  "  over  fat  "  those  who 
exceed  by  more  than  30  per  cent,  i.e.  over  155  pounds  for  a 
woman  5  feet  3  inches  or  over  195  pounds  for  a  man  5  feet  8 
inches. 

Symonds  has  published*  the  average  relation  of  height  to 
weight  in  both  men  and  women  at  different  ages,  as  computed 
from  the  records  of  accepted  applicants  for  life  insurance  in 
the  United  States  and  Canada.  The  results  are  found  in  the 
following  tables;  that  for  men  being  based  on  74,162  and  that 
for  women  on  58,855  cases.  In  all  these  cases  the  height  in- 
cludes shoes  and  the  weight  includes  ordinary  clothing. 

Symonds's  Table  of  Height  and  Weight  for  Men  at  Different  Ages 

based  on  74,162  accep-j^d  applicants  for  life  insurance 

{Medical  Record) 


Ages 

15-24 

25-29 

30-34 

35-39 

40-44 

45-49 

50-54 

55-59 

60-64 

65-^9 

5  ft. 

0  in. 

120 

125 

128 

131 

133 

134 

134 

134 

131 

I  in. 

122 

126 

129 

131 

134 

136 

136 

136 

134 

2  in. 

124 

128 

131 

133 

136 

138 

138 

138 

137 

3  in. 

127 

131 

134 

136 

139 

141 

141 

141 

140 

140 

4  m. 

131 

^35 

138 

140 

143 

144 

145 

145 

144 

143 

5  in. 

134 

138 

141 

143 

146 

147 

149 

149 

148 

147 

6  in. 

138 

142 

145 

147 

150 

151 

153 

153 

153 

151 

7  in. 

142 

147 

150 

152 

155 

156 

158 

158 

158 

156 

Sin. 

146 

151 

154 

157 

160 

161 

163 

163 

163 

162 

9  in. 

150 

155 

159 

162 

165 

166 

167 

168 

168 

168 

10  in. 

154 

159 

164 

167 

170 

171 

172 

173 

174 

174 

II  in. 

159 

164 

169 

173 

175 

177 

177 

178 

180 

180 

6  ft. 

0  in. 

165 

170 

175 

179 

180 

183 

182 

183 

185 

i8s 

I  m. 

170 

177 

181 

185 

186 

189 

188 

189 

189 

189 

2  in. 

176 

184 

188 

192 

194 

196 

194 

194 

192 

192 

3  m. 

181 

190 

195 

200 

203 

204 

201 

198 

*  Medical  Record,  September  5,  1908;  and  McClure's  Magazine,  January,  1909. 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      369 


Symonds's  Table  of  Height  and  Weight  for  Women  at  Different 

Ages 

based   on   58,855    ACCEPTED   APPLICANTS   FOR  LIFE   INSURANCE 

(McClure's  Magazine) 


Ages 

1S-19 

20-24 

25-29 

30-34 

35-39 

40-44 

45-49 

So*54 

55-59 

60-64 

4 

ft.  II  in. 

III 

113 

115 

117 

119 

122 

125 

128 

128 

126 

5 

ft.  0  in. 

113 

114 

117 

119 

122 

125 

128 

130 

131 

129 

I  m. 

115 

116 

118 

121 

124 

128 

131 

133 

134 

132 

2  m. 

117 

118 

120 

123 

127 

132 

134 

137 

137 

136 

3in- 

120 

12  2, 

124 

127 

131 

13'? 

138 

141 

141 

140 

4  in. 

^ 

125 

127 

130 

134 

138 

142 

145 

145 

144 

Sm* 

I2S. 

128 

131 

135 

139 

143 

147 

149 

149 

148 

6  in. 

128 

132 

135 

137 

143 

146 

151 

153 

153 

152 

7  in. 

132 

135 

139 

143 

147 

150 

154 

157 

156 

IS."? 

Sin. 

136 

140 

143 

147 

151 

155 

158 

161 

161 

160 

9  in. 

140 

144 

147 

151 

15s 

159 

163 

166 

166 

165 

10  in. 

144 

147 

151 

155 

159 

163 

167 

170 

170 

169 

From  a  study  of  the  records  of  body  weight  in  relation  to 
the  mortality  records  Symonds  concludes  that  among  young 
people  the  greatest  vitality  coincides  with  a  weight  somewhat 
above  the  accepted  average,  while  with  middle-aged  and 
elderly  people  a  condition  of  slightly  less  than  average  fatness 
is  most  favorable  to  vitality  and  longevity.  Another  way  of 
stating  the  same  facts  is:  That  the  average  of  healthy  men 
and  women  keep  themselves  slightly  too  thin  while  young, 
and  allow  themselves  to  grow  slightly  too  stout  as  they  grow 
older. 

Evidently,  however,  the  optimum  is  very  near  the  average 
of  the  accepted  applicants  as  shown  in  the  tables,  and  Symonds 
uses  these  figures  as  standards  in  his  computations  and  dis- 
cussions of  the  influence  of  overweight  and  underweight  on 
longevity  and  on  mortality  from  specific  diseases.  Symonds's 
data  therefore  support  the  opinion  that  the  average  degree  of 


2B 


370  CHEMISTRY  OF  FOOD  AND  NUTRITION 

fatness  of  healthy  American  people  is  just  about  the  most 
advantageous  fatness  for  them  to  maintain.  Whatever  we 
accept  as  the  ideal  relation  of  weight  to  height,  it  is  obvious 
that  the  proper  standard  for  fuel  value  of  the  diet  is  that  which 
will  preserve  the  desired  degree  of  fatness  while  sustaining  the 
desired  amount  of  activity.  If  good  authorities  differ  in 
standards  for  fuel  value,  it  is  because,  consciously  or  uncon- 
sciously, they  contemplate  different  amounts  of  muscular 
activity  or  the  maintenance  of  a  different  physique. 

That  the  amount  of  food  required  per  day  to  maintain  a 
healthy  adult  at  the  desired  body  weight  will  vary  considerably 
with  age  and  size  and  enormously  with  extremes  of  muscular 
activity  has  already  been  explained  at  some  length  in  Chapter 
VII  and  need  not  be  discussed  further  here.  Unless  it  is  desired 
to  increase  or  decrease  the  body  weight,  the  optimum  energy 
intake  of  the  healthy  adult  will  be  that  which  coincides  with  the 
total  energy  expenditure ;  in  other  words  the  "  standard  " 
and  the  "  requirement  "  will  in  this  case  be  the  same. 

Energy  Allowances  for  Children 

Food  allowances  or  dietary  standards  for  children  differ 
from  those  for  adults  -in  that  they  must  provide  not  only  for  all 
expenditures  but  also  for  growth.  Recently  a  considerable 
number  of  accurate  measurements  of  energy  expenditure  of 
children  have  been  made  —  especially  of  infants  in  the  first 
year  of  life  and  of  boys  twelve  and  thirteen  years  old.  These 
data  whether  obtained  by  the  method  of  direct  or  indirect 
calorimetry  give  precise  information  as  to  the  energy  output 
at  the  time  of  the  experiment,  but  naturally  the  observations 
cannot  cover  the  entire  24  hours  of  the  day,  nor  can  experiments 
of  a  few  hours'  duration  give  any  direct  information  as  to  how 
much  the  intake  must  exceed  the  output  in  order  to  provide 
amply  for  a  normal  rate  of  growth.  Observations  of  the  un- 
restricted   food    consumption    (ordinary    dietary    studies)    of 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      371 

healthy  children  who  are  making  normal  growth,  and  nitrogen 
balance  experiments  which  show  both  gain  in  weight  and  storage 
of  nitrogen  (growth  of  protein  tissue)  may  be  expected  to  furnish 
evidence  of  some  value  though  of  a  somewhat  inferential  nature. 
As  a  result  of  compilation  and  study  of  all  available  data  whether 
of  dietary  studies,  nitrogen  balance  experiments,  observations 
of  the  respiratory  exchange,  or  direct  measurements  of  energy 
output,  the  following  standards  are  suggested : 


Food  Allowances  for  Healthy  Children  (Gillett) 


Age 

Calories  per  Day 

Years 

Boys 

Girb 

Under  2 

900-1200 

900-1200 

2-3 

1000-1300 

980-1280 

3-4 

I 100-1400 

1060-1360 

4-S 

I 200-1 500 

I 140-1440 

5-6 

I 300-1 600 

1220-1520 

6-7 

1400-1 700 

1300-1600 

7-8 

I 500-1 800 

1380-1680 

8-9 

I 600-1 900 

1460-1760 

9-10 

1700-2000 

1550-1850 

lO-II 

1900-2200 

1650-1950 

11-12 

2100-2400 

1750-2050 

12-13 

2300-2700 

I 850-2 I 50 

13-14 

2500-2900 

1950-2250 

14-1S 

2600-3100 

2050-2350 

15-16 

2700-3300 

2150-2450 

16-17 

2700-3400 

2250-2500 

In  earlier  allowances  no  distinction  was  made  between  boys 
and  girls  below  ten  years. of  age.  The  averages  of  recorded 
data  show,  however,  a  slightly  higher  energy  exchange  (or 
metabolism)  in  boys  than  in  girls  of  the  same  age,  though 
the  difference  is  often  less  than  the  range  allowed  to  cover 
differences  of  size  and  activity  at  a  given  age.     Beyond  10 


372 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


years  of  age,  the  energy  exchange  in  boys  evidently  increases 
more  rapidly  than  in  girls,  probably  because  of  their  greater 
restlessness  and  muscular  activity  through  this  period  of  de- 
velopment and  their  greater  average  rate  of  growth  during 
and  after  the  fifteenth  year. 

In  this  connection  the  accompanying  table  adapted  from  that 
of  Manny  based  on  data  from  Holt,  Burt,  and  Boas  is  of  interest. 

Average  Weights  and  Rates  of  Growth  of  Boys  and  Girls  at 
Different  Ages  (Manny) 


Boys 

Girls 

Age 

Weight 

Increase 

Weight 

Increase 

Per 

Per 

Per 

Per 

Kgms. 

Lbs. 

Year 
Lbs. 

Week 
Grams 

Kgms. 

Lbs. 

Year 
Lbs. 

Week 
Grams 

At  birth       .     . 

3.43 

7.55 

3.25 

7.16 

6  months 

7.27 

16.00 

16.90 

147 

7.05 

15.50 

16.68 

145 

I  year 

9-32 

20.50 

9.00 

78 

9.00 

19.80 

8.60 

75 

2  years 

12.05 

26.50 

6,00 

52 

11.59 

25.50 

5.70 

50 

3  years 

14.18 

31.20 

4.70 

41 

13.63 

30.00 

4.50 

39 

4  years 

15.91 

35.00 

3.80 

33 

15.45 

34.00 

4.00 

35 

5  yr.  6  mo. 

18.73 

41.20 

4.13 

36 

18.09 

39.80 

3.87 

34 

6  yr.  6  mo. 

20.55 

45.20 

4.00 

35 

19.73 

43.40 

3.60 

31 

7  yr.  6  mo. 

22,50 

49.50 

4.30 

38 

21.68 

47.70 

4.30 

38 

8  yr.  6  mo. 

24.77 

54.50 

5.00 

44 

23.86 

52.50 

4.80 

42 

9  yr.  6  mo. 

27.09 

59.60 

5.10 

45 

26.09 

57.40 

4.90 

43 

lo  yr.  6  mo. 

29.73 

65.40 

5.80 

51 

28.59 

62.90 

5.50 

48 

II  yr.  6  mo. 

32.14 

70.70 

5.30 

46 

31.59 

69.50 

6.60 

S8 

12  yr.  6  mo. 

34.95 

76.90 

6.20 

54 

35.77 

78.70 

9.20 

80 

13  yr.  6  mo. 

38.55 

84.80 

7.90 

69 

40.32 

88.70 

10,00 

87 

14  yr.  6  mo. 

43.27 

95.20 

10.40 

91 

44.68 

98.30 

9.60 

84 

15  yr.  6  mo. 

48.82 

107.40 

12.20 

107 

48.50 

106.70 

8.40 

73 

16  yr.  6  mo 

55.00 

121.00 

13.60 

119 

51.02 

112.30 

5.60 

49 

Children,  like  adults,  will  vary  in  muscular  activity  and  this 
will  influence  their  energy  requirements  irrespective  of  other 
conditions.  Among  other  conditions  to  be  considered  are 
differences  in  size  and  physical  development  among  children 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      373 

of  the  same  age  and  sex.  Children  of  more  than  average  size,  if 
normally  active  and  not  over-fat,  will  require  somewhat  more 
food  than  an  average  child  of  the  same  age.  An  estimate  of 
energy  requirement  per  unit  of  weight  at  different  ages  has 
been  given  in  Chapter  VII  (page  196).  A  child  who  has  become 
somewhat  emaciated,  either  through  rapid  growth  *  or  other 
causes,  should  have  a  larger  food  allowance  than  would  ordinarily 
be  required  either  for  his  age  or  for  his  weight. 

In  calculating  the  food  requirements  of  a  family  it  is  best 
not  to  estimate  the  needs  of  other  members  in  terms  of  that  of 
the  man  of  the  family  (because  men  on  account  of  the  great 
differences  in  activity  of  their  occupations  are  hkely  to  be  more 
variable  in  their  energy  requirements  than  are  children  of  any 
given  age)  but  rather  to  estimate  the  Calories  for  each  mem- 
ber of  the  family  separately  according  to  his  or  her  own  needs 
and  then  sum  up  the  total.  Not  infrequently  other  members 
of  the  family  may  require  more  food  than  the  maUj  especially 
if  he  be  of  less  than  average  size  and  engaged  in  sedentary  or 
other  light  work. 

The  Problem  of  a  Standard  for  Protein 

In  attempting  to  set  a  standard  for  the  amount  of  protein  in 
the  dietary  we  find  no  such  definite  and  satisfactory  basis  for 
judgment  as  in  the  case  of  total  food  (or  fuel)  value.  There  is 
no  indication  that  any  kind  of  work  necessarily  increases  the 

*  Large  as  are  the  appetites  of  growing  children  it  is  not  uncommon  for  the 
"growth  impuke"  to  outrun  the  food  intake  so  that  the  child  although  always  having 
had  access  to  ample  food  may  as  the  result  of  very  rapid  growth  be  brought  into  a 
condition  somewhat  resembling  that  of  the  young  animals  described  in  the  preceding 
chapter  (page  338)  which  become  emaciated  through  "attempting  to  grow"  on 
rations  sufficient  only  for  maintenance,  i.e.  through  the  growth  of  some  tissues  at 
the  expense  of  others.  As  Aron-  points  out  a  child  in  this  condition  has  an  abnor- 
mally low  percentage  of  fat  and  high  percentage  of  water  in  his  body  content. 
Hence  he  needs  extra  fotd  not  only  to  increase  his  weight  up  to  that  which  corre- 
sponds to  his  height,  but  also  to  restore  the  normal  percentage  of  fat  in  the  body 
weight  which  he  already  has. 


374  CHEMISTRY  OF  FOOD  AND   NUTRITION 

expenditure  of  protein  as  muscular  work  increases  the  expendi- 
ture of  fuel,  and  the  body  cannot  store  up  protein  to  anything 
like  the  extent  that  it  stores  fuel  in  the  form  of  fat ;  the  feeding 
of  protein  above  what  is  required  for  maintenance  increases 
only  slightly  the  store  of  protein  which  the  body  carries. 

When  one  writer  proposes  an  amount  of  protein  but  little 
above  the  minimum  required  for  equilibrium,  while  another 
advocates  a  much  larger  amount,  there  is  implied  a  difference 
of  view  regarding  protein  such  as  no  longer  exists  with  respect 
to  the  energy  metabolism.  The  difference,  it  is  true,  is  hardly 
so  great  as  might  appear  from  a  casual  examination  of  the  pro- 
posed standards.  It  may  perhaps  be  most  fairly  expressed 
in  terms  of  the  relation  between  protein  and  energy  in  the 
different  standards.  Protein  would  contribute,  according  to  the 
standards  of  Voit,  Playfair,  and  Gautier,  about  i6  per  cent  of 
the  fuel  value  of  the  food;  of  Atwater,  about  15  per  cent;  of 
Langworthy,  12  per  cent;  of  Chittenden,  8^  per  cent. 

It  will  be  of  interest  to  examine  some  of  the  arguments  which 
have  been  advanced  in  favor  of  a  high  protein  or  of  a  low  pro- 
tein diet.  The  following  extracts,  given  in  chronological  order, 
are  from  writings  of  those  who  had  given  special  study  to  the 
subject  and  chiefly  from  the  literature  of  the  first  decade  of  this 
century,  when  Chittenden's  investigation  of  the  protein  require- 
ment was  a  subject  of  active  discussion.  The  time  of  publica- 
tion of  these  opinions  must  not  be  overlooked,  since  some  of 
the  phenomena  then  attributed  to  differences  in  protein  intake 
might  perhaps  now  be  attributed,  in  part  at  least,  to  the  ash 
constituents  and  vitamines  of  the  food. 

Opinions  regarding  the  Value  of  Liberal  Protein  Diet 

Liebig  believed  that  fats  and  carbohydrates  were  burned  in 
the  body  primarily  to  supply  it  with  warmth,  and  that  protein 
alone  served  as  the  source  of  muscular  work  and  other  forms  of 
tissue  activity.     He  therefore  classed  the  non-nitrogenous  as 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD     375 

''  respiratory  "  and  the  nitrogenous  as  "  plastic  "  foodstuffs,  and 
treated  the  proteins  as  playing  a  "  nobler  "  part  in  nutrition  than 
can  be  taken  by  fat  or  carbohydrate.  Although  it  was  soon 
demonstrated  that  carbohydrates  and  fats  as  well  as  protein 
serve  the  body  in  the  production  of  muscular  energy,  yet  the 
influence  of  Liebig's  teaching,  and  of  the  great  attention  given 
to  protein  in  Voit's  classical  researches  on  nutrition,  together 
with  the  fact  that  protein  is  the  most  prominent  constituent  of 
protoplasm,  has  resulted  in  a  strong  tendency  to  associate  high 
protein  feeding  with  increased  stamina  and  muscular  power. 

The  reasoning  of  those  who  appreciated  the  results  of  more 
recent  experimental  work,  and  yet  believed  the  general  attitude 
of  Liebig  and  Voit  to  have  been  largely  sustained  by  experience, 
is  well  expressed  by  Von  Noorden,  who  wrote  in  1893  :  * 

"  When  one  considers  that  the  dietary  habits  of  peoples  are 
the  results  of  biological  laws,  it  would  seem  that  the  action  of 
these  laws,  extending  through  the  thousands  of  years  of  existence 
of  the  species,  would  have  resulted  in  the  establishment  of  suit- 
able habits  regarding  the  amounts  of  protein  consumed.  The 
data  gathered  by  Voit  may  be  taken  as  showing  that  this 
normal  habit  involves  the  consumption  of  about  105  grams  of 
digestible  protein  f  per  day,  a  smaller  protein  consumption 
being  usually  associated  with  weak  individuals  or  inactive 
peoples.  While  men  can  maintain  equilibrium  on  less,  still 
it  can  rightly  be  said  that  a  liberal  protein  consumption  makes 
for  a  full  development  of,  the  man.  A  single  individual  may 
for  years,  or  even  decades,  offend  against  this  biological  law 
unpunished.  When,  however,  the  small  consumption  of  protein 
continues  for  generations,  there  results  a  weak  race." 

Von  Noorden,  however,  is  careful  to  add : 

*  Freely  translated  from  the  first  edition  of  Von  Noorden's  Pathologic  der  Stoff- 
wechsel. 

t  Corresponding  to  Vtit's  allowance  of  118  grams  of  total  protein  when  the  food 
for  the  sake  of  economy,  as  contemplated  by  V^oit,  is  taken  somewhat  largely  from 
vegetable  sources. 


376  CHEMISTRY  OF  FOOD  AND   NUTRITION 

"  On  the  other  hand,  the  importance  of  protein  must  not  be 
overestimated.  A  diet  is  not  necessarily  good  because  the 
amount  of  protein  is  right ;  it  must  have  the  proper  proportions 
of  the  non-nitrogenous  nutrients  as  well,  since  the  protein  is  not 
to  be  depended  upon  for  the  necessary  fuel  value.  Better 
somewhat  less  protein  with  a  liberal  amount  of  total  food  than 
more  protein  with  insufficient  fuel  value;  the  latter  brings  a 
rapid  loss  of  strength,  the  former  can  be  endured  very  well,  at 
least  for  a  long  time,  and  very  likely  throughout  the  life  of  the 
individual." 

Chittenden,  in  1905,  had  reached  exactly  the  opposite  conclu- 
sion, —  that  the  products  of  protein  metabolism  are  a  constant 
menace  to  the  well-being  of  the  body,  and  that  any  excess  of 
protein  over  what  the  body  actually  needs  is  likely  to  be  directly 
injurious,  and  at  best  puts  an  unnecessary  and  useless  strain 
upon  the  Uver  and  kidneys.  Chittenden  had  satisfied  himself 
by  his  numerous  and  long-continued  experiments  that  both 
physical  and  mental  stamina  are  promoted  by  decreasing  the 
amount  of  protein  in  the  food :  ''  Greater  freedom  from  fatigue, 
greater  aptitude  for  work,  greater  freedom  from  minor  ailments, 
have  gradually  become  associated  in  the  writer's  mind  with  this 
lowered  protein  metabolism  and  general  condition  of  physiologi- 
cal economy  "...  {Physiological  Economy  in  Nutrition,  pages 
51,  127). 

Hutchison,  in  1906,  concluded  that  the  normal  amount 
of  protein  in  a  diet  furnishing  3000  Calories  should  be  placed 
at  about  75  grams.  This  allows  some  margin  above  the 
results  of  Chittenden's  experiments  and  agrees  with  the  rela- 
tion of  protein  to  calories  in  mother's  milk,  which  Hutchison 
regards  as  nature's  hint  as  to  the  proper  balance  of  nitroge- 
nous and  non-nitrogenous  -food  for  the  human  species  {Chemi- 
cal News,  Vol.  94,  page  104). 

Folin  held  that  the  argument  for  a  high  protein  diet  based 
on  the  fact  that  large  amounts  of  protein  are  commonly  eaten 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD     377 

by  those  who  can  afford  it  can  be  equally  well  appUed  to  the 
dietetic  use  of  alcoholic  beverages  and  is  no  more  convincing 
in  one  case  than  in  the  other ;  while  on  the  other  hand,  study  of 
protein  metaboHsm  has  given  rather  strong  evidence  that  the 
body  has  no  need  of  such  amounts  as  are  commonly  eaten. 
The  loss  of  body  nitrogen  which  occurs  iii  the  early  periods  of 
restricted  protein  feeding,  and  which  was  not  determined  nor 
specifically  discussed  by  Chittenden,  is  treated  by  Folin  as 
follows :  "  All  the  living  protoplasm  in  the  animal  organism  is 
suspended  in  a  fluid  veiy  rich  in  protein,  and  on  account  of  the 
habitual  use  of  more  nitrogenous  food  than  the  tissues  can  use 
as  protein,  the  organism  is  ordinarily  in  possession  of  approxi- 
mately the  maximum  amount  of  reserve  protein  in  solution  that 
it  can  advantageously  retain.  When  the  supply  of  food  protein 
is  stopped,  the  excess  of  reserved  protein  inside  the  organism  is 
still  sufficient  to  cause  a  rather  large  destruction  of  protein 
during  the  first  day  or  two  of  protein.  sJbarvation,  and  after  that 
the  protein  catabolism^i^j^ygry  smaTf,  provided  sufficient  non- 
nitrogenous  Jo^d-'is  '^?tf!Sfefe.  But  even  then,  and  for  many 
days  thereafter,  the  protoplasm  of  the  tissues  has  still  an 
abundant  supply  of  dissolved  protein,  and  the  normal  activity  of 
such  tissues  as  the  muscles  is  not  at  all  impaired  or  diminished. 
When  30  grams  or  40  grams  of  nitrogen  have  been  lost  by  an 
average-sized  man  during  a  week  or  more  of  abstinence  from 
nitrogenous  food  (but  with  an  abundance  of  carbohydrate  and 
fat)  the  hving  muscle  tissues  are  still  well  suppHed  with  all  the 
protein  that  they  can  use.  .  .  .  The  continuous  excessive 
use  of  protein  may  lead,  however,  to  an  accumulation  of  a  larger 
amount  of  reserve  protein  than  the  organism  can  with  advantage 
retain  in  its  fluid  media.  It  is  entirely  possible  that  the  con- 
tinuous maintenance  of  such  an  unnecessarily  large  supply  of 
unorganized  reserve  material  may  sooner  or  later  weaken  one, 
or  another,  or  all,  of  the  hving  tissues.  At  any  rate,  it  seems 
scarcely  conceivable  that  the  human  organism,  having  all  the 


378  CHEMISTRY  OF  FOOD  AND  NUTRITION 

time  access  to  food,  can  gain  in  efficiency  on  account  of  such  an 
excess  of  stored  protein.  The  carrying  of  excessive  quantities 
of  fat  is  considered  as  an  impediment,  the  carrying  of  exces- 
sive quantities  of  unorganized  protein  may  be  none  the  less  so 
because  more  common  and  less  strikingly  apparent"  {American 
Journal  of  Physiology,  Vol.  13,  pages  131-132,  136-137). 

Benedict  argued  that  general  experience  in  animal  feeding 
favors  the  use  of  liberal  quantities  of  protein,  and  that  "  while 
men  may  for  some  months  reduce  the.  proportion  of  protein  in 
their  diet  very  markedly  and  apparently  suffer  no  deleterious 
consequences,  yet,  nevertheless,  a  permanent  reduction  of  the 
protein  beyond  that  found  to  be  the  normal  amount  for  man  is 
not  without  possible  danger.  The  fact  that  a  subject  can  so 
adjust  an  artificial  diet  as  to  obtain  nitrogenous  equiHbrium  with 
an  excretion  of  nitrogen  amounting  to  about  2  or  3  grams  per 
day  is  no  logical  argument  for  the  permanent  reduction  of  the 
nitrogen  in  food  for  the  period  of  a  lifetime.  .  .  .  Dietary 
studies  all  over  the  world  show  that  in  those  communities  where 
productive  power,  enterprise,  and  civilization  are  at  their  high- 
est, man  has  instinctively  and  independently  selected  Hberal 
rather  than  small  quantities  of  protein "  {American  Journal 
of  Physiology,  Vol.  16,  page  409). 

A  similar  position  was  taken  by  Meltzer,  who  compared  the  ap- 
petite for  a  Hberal  surplus  of  protein  with  the  Hberal  way  in  which 
the  body  is  provided  with  organs  and  tissues  for  nearly  all  of  its 
functions,  and  concludes  that  "  valuable  as  the  facts  which  Chit- 
tenden and  his  colaborer  found  may  be,  they  do  not  make 
obvious  their  theory  that  the  minimum  supply  is  the  optimum  — 
the  ideal.  The  bodily  health  and  vigor  which  people  with  one 
kidney  still  enjoy  does  not  make  the  possession  of  only  one 
kidney  an  ideal  condition.  The  finding  that  the  accepted 
standard  of  protein  diet  can  be  reduced  to  one  half  can  be  com- 
pared with  the  finding  that  the  inspired  oxygen  can  be  reduced 
to  one  half  without  affecting  the  health  and  comfort  of  the 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      379 

individual,  but  no  one  deduces  from  the  latter  fact  that  the 
breathing  of  air  so  rarefied  would  be  the  ideal.  .  .  .  The 
storing  away  of  protein,  like  the  storing  away  of  glycogen  and 
fat,  for  use  in  expected  and  unexpected  exceptional  conditions 
is  exactly  like  the  superabundance  of  tissues  in  an  organ  of  an 
animal,  or  like  an  extra  beam  in  the  support  of  a  building  or  a 
bridge  —  a  factor  of  safety  "  {Science,  Vol.  25,  page  481). 

In  view  of  the  arguments  of  Benedict  and  of  Meltzer,  it  is  of 
especial  interest  that  in  his  later  book  Chittenden  says:  "  It  is 
certainly  just  as  plausible  to  assume  that  increase  in  the  con- 
sumption of  protein  food  follows  in  the  footsteps  of  commercial 
and  other  forms  of  prosperity,  as  to  argue  that  prosperity  or 
mental  and  physical  development  are  the  result  of  an  increased 
intake  of  protein  food.  Protein  foods  are  usually  costly  and  the 
ability  of  a  community  to  indulge  freely  in  this  form  of  dietetic 
luxury  depends  in  large  measure  upon  its  commercial  pros- 
perity." Moreover,  Chittenden  contends  that  his  allowance  of 
60  grams  of  protein  per  day  for  a  man  of  average  size  is  a 
perfectly  trustworthy  figure,  with  a  reasonable  margin  of 
safety ;  that  "  dietetic  requirements,  and  standard  dietaries, 
are  not  to  be  founded  upon  the  so-called  cravings  of  appetite, 
but  upon  reason  and  intelligence  reenforced  by  definite  knowl- 
edge of  the  real  necessities  of  the  bodily  machinery"  ;  that  "  we 
must  be  ever  mindful  of  the  fact,  so  many  times  expressed,  that 
protein  does  not  undergo  complete  oxidation  in  the  body  to 
simple  gaseous  products  like  the  non-nitrogenous  foods,  but 
that  there  is  left  behind  a  residue  not  so  easily  disposed  of  " ; 
and  that  "  there  are  many  suggestions  of  improvement  in  bodily 
health,  of  greater  efiiciency  in  working  power,  and  of  greater 
freedom  from  disease,  in  a  system  of  dietetics  which  aims  to  meet 
the  physiological  needs  of  the  body  without  undue  waste  of 
energy  and  unnecessary  drain  upon  the  functions  of  digestion, 
absorption,  excretion,  and  metabohsm  in  general  ..."  {The 
Nutrition  of  Man,  pages  160,  164,  227,  269). 


380  CHEMISTRY  OF  FOOD  AND   NUTRITION 

Plainly  the  dietary  habit  of  well-to-do  people  and  the  diet- 
ary standards  which  have  been  generally  accepted  in  the  past 
tend  to  be  decidedly  liberal  with  respect  to  protein,  and  to 
prescribe  it  in  quantities  which  may  be  believed  to  be  benefi- 
cial but  certainly  are  not  known  to  be  necessary.  It  does  not 
seem  advisable,  however,  to  adopt  as  a  standard  the  lowest 
amount  of  protein  to  which  the  body  can  adjust  itself,  but 
rather  to  regard  as  the  normal  requirement  an  amount  which 
will  enable  the  body  to  maintain  not  only  its  equilibrium, 
but  also  some  such  reserve  store  of  protein  as  we  are  accustomed 
to  carry.  An  allowance  of  about  75  grams  of  protein  per 
man  per  day,  which  is  50  per  cent  above  the  average  estimate 
of  actual  requirement  (page  220),  seems  fully  adequate  in  view 
of  our  present  knowledge. 

A  reasonable  surplus  of  protein,  from  suitable  food  materials, 
can  hardly  be  injurious  and  may  be  advantageous.  Whether 
such  a  surplus  should  be  especially  recommended  or  not  is 
largely  an  economic  question.  Where  Httle  can  be  spent  for 
food  and  there  is  danger  that  too  little  food  may  be  eaten, 
it  would  be  a  mistake  to  use  a  surplus  of  protein  which  could 
economically  be  replaced  by  other  food  of  greater  fuel  value. 
In  such  cases  one  must  not  be  misled  by  the  popular  state- 
ment that  "  protein  builds  tissue  "  into  supposing  that  a  lib- 
eral amount  of  protein  can  keep  the  body  strong  in  spite  of  a 
deficiency  in  the  total  food.  This  impression  is  still  somewhat 
prevalent,  but  is  certainly  incorrect. 

The  body  is  weakened  through  getting  too  little  food,  be- 
cause body  material  must  then  be  burned  for  fuel.  So  long  as 
the  total  food  be  deficient,  the  loss  of  body  substance  will 
continue,  because  not  only  the  food  protein,  but  body  tissues 
as  well,  must  be  burned  to  meet  the  energy  requirement.  To 
strengthen  the  body  through  the  diet  we  must  increase,  not  the 
protein  alone,  but  primarily  the  total  calories. 

Strengthening  or  weakening  of  the  body  by  feeding  ordi- 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      381 

narily  depends  much  more  upon  the  sufficiency  or  insufficiency 
of  the  energy  value  of  the  total  food  than  upon  the  amount  of 
protein  which  it  contains. 

Protein  Standards  for  Children  and  for  Family  Dietaries 

Little  can  be  said  with  confidence  regarding  the  best  amount 
of  protein  for  children  after  the  nursing  period.  In  practice 
well-planned  dietaries  for  children  usually  contain  between  10 
and  15  per  cent  of  the  total  energy  in  the  form  of  protein. 
During  the  years  of  rapid  growth  a  considerable  fraction  of 
the  protein  of  the  food  is  utilized  in  the  synthesis  of  body  pro- 
teins ;  and  since  the  amount  of  food  protein  required  to  form  a 
gram  of  body  protein  is  variable,  depending  upon  the  amino  acid 
make-up  of  the  former,  it  is  evident  that  the  kind  of  protein 
supplied  becomes  a  matter  of  great  importance.  Here  chemical 
and  physiological  laboratory  evidence,  cHnical  experience,  and 
its  evident  place  in  nature  all  indicate  plainly  the  superiority 
of  milk  as  source  of  supply  of  protein  for  growth,  whether  the 
case  be  that  of  the  growing  child  after  weaning  or  of  the  nursling 
fed  through  the  mother.  The  recommendation  that  family 
dietaries  should  whenever  possible  include  "  a  quart  of  milk 
a  day  for  every  child  "  was  aimed  primarily  to  insure  an  appro- 
priate protein  supply.  Needless  to  say,  the  milk  also  supplies 
important  amounts  of  many  other  substances  essential  to  growth. 

Since  the  energy  requirement  is  greatly  increased  by  muscular 
activity  and  the  protein  requirement  is  not,  it  is  evident  that  in 
the  metaboHsm  of  normal  adults  the  energy  and  protein  require- 
ments will  not  run  parallel.  The  protein  requirement  of  the 
healthy  adult  depends  chiefly  upon  his  size,  while  his  energy 
requirement  depends  chiefly  upon  his  activity. 

In  childhood  both  the  energy  requirement  and  the  protein 
requirement  are  high  —  often  two  to  three  times  as  high  per 
unit  of  weight  as  for  adults  without  muscular  work.  More- 
over the  high  protein  and  energy  requirements  of  the  child  as 


382  CHEMISTRY  OF  FOOD  AND   NUTRITION 

compared  with  the  man  are  found  to  run  approximately  parallel 
and  as  shown  in  a  previous  chapter  the  same  proportion  of  pro- 
tein in  terms  of  the  total  energy  which  seems  rational  for  the 
adult  dietary  suffices  also  for  the  food  requirements  of  the  child 
provided  in  the  latter  case  the  food  is  of  appropriate  kind. 

In  most  family  groups  the  differences  in  age  and  size  will 
constitute  a  more  prominent  factor  than  the  differences  in 
activity,  and  since  the  former  affect  energy  and  protein  require- 
ments in  about  the  same  proportion,  it  becomes  feasible  and 
convenient  to  set  the  protein  allowance  for  ordinary  family 
groups  in  terms  of  a  proportion  of  the  total  food  value.  To 
allow  for  varying  conditions  and  for  individual  preferences 
as  well  as  to  provide  a  liberal  margin  for  safety  it  is  customary 
to  consider  that  from  10  to  15  per  cent  of  the  total  calories  may 
be  in  the  form  of  protein. 

In  cases  where  the  nutritive  requirements  of  growth,  preg- 
nancy, or  lactation  are  to  be  met,  the  kind  of  protein  is  perhaps 
as  important  as  the  amount. 

Standards  for  the  Calcium,  Phosphorus,  and  Iron  Content  of 

the  Dietary 

Formerly  dietary  standards  took  no  account  of  the  ash 
constituents  because  it  was  assumed  that  dietaries  furnishing 
sufficient  energy  and  protein  would  always  be  adequate  as 
regards  the  "  inorganic  "  elements.  As  explained  in  previous 
chapters  this  assumption  is  not  safe  in  the  case  of  calcium, 
phosphorus,  or  iron.  In  the  light  of  present  knowledge  ade- 
quate dietary  standards  must  provide  for  these  elements.  The 
experimental  evidence  regarding  the  minimum  requirements  of 
the  body  for  each  of  these  elements  has  been  reviewed  in  earUer 
chapters  and  there  has  been  but  brief  discussion  of  the  relation 
between  minimum  and  optimum  amounts. 

The  evidence  thus  far  available  indicates  an  average  minimum 
requirement  for  equilibrium,  per  man  per  day,  of  0.45  gram 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      383 

calcium  (0.63  gram  CaO),  0.96  gram  phosphorus  (2.20  grams 
P2O5),  and  about  o.oio  gram  (10  miUigrams)  of  iron. 

To  allow  only  these  quantities  in  the  daily  food  would  corre- 
spond to  an  allowance  of  only  50  grams  per  man  per  day  of  protein. 

If  the  standard  allowance  be  set  50  per  cent  above  the  indi- 
cated average  minimum  corresponding  to  an  allowance  of  75 
grams  of  protein  we  obtain 

Calcium,       0.68    gram  (equivalent  to  0.95  gram  of  calcium 

oxide,  CaO). 
Phosphorus,  1.44    grams  (equivalent  to  3.30  grams  of  P2O5). 
Iron,  0.015  gram  (15  milligrams). 

If  these  be  taken  as  proper  allowances  per  man  of  70  kilograms 
whose  energy  requirement  averages  3000  Calories  per  day, 
then  the  corresponding  allowances  for  other  adults  or  for  famiUes 
containing  children  could  also  be  stated  as  follows : 


For  Adults 

PER  Kilogram  of 

Body  Weight 

For  Children  (or 

Families  Containing 

Children)  per 

100  Calories 

Protein 

Phosphorus 

Calcium 

Iron 

1.07        grams 
0.0206    gram 
0.0097    gram 
0.00022  gram 

2.5  *     grams  ' 
0.048    gram 
0.023    gram 
0.0005  gram 

If  it  be  desired  to  provide  as  liberal  a  margin  of  safety  here 
as  in  the  case  of  a  protein  allowance  of  100  grams  per  man  per 
day,  then  the  above  figures  must  obviously  be  increased  by  one 
third. 

The  Unidentified  Essentials 

Of  the  unidentified  fat-soluble  and  water-soluble  substances 
essential  to  normal  metaboUsm  we  have  as  yet  no  direct  quanti- 
tative measures,  eithsr  of  the  proportions  in  which  they  occur 
in  food  or  are  needed  in  nutrition.     In  view  of  their  importance 
*  In  the  case  of  the  child  this  should  be  mainly  milk  protein. 


384  CHEMISTRY  OF  FOOD  AND  NUTRITION 

it  is  plain  that  they  should  not  be  ignored  in  the  planning  of 
dietaries,  either  of  children  or  adults.  McCollum  and  Sim- 
monds  have  recently  shown  that  a  low  intake  of  either  "  fat 
soluble  A  "  or  "  water  soluble  B  "  not  only  retards  or  suspends 
the  growth  of  young  animals  but  is  also  distinctly  detrimental 
to  adults.  A  diet  furnishing  barely  enough  of  these  essentials 
to  support  slow  growth  of  young  regularly  resulted  in  sub- 
normal vitality  when  fed  to  adults;  but  the  symptoms  were 
not  always  the  same,  e.g.  some  of  the  adults  lost  weight 
while  others  maintained  weight  but  lost  vitaHty.  They  state : 
"  Our  results  indicate  that  there  is  no  low  plane  of  intake  of 
either  of  these  substances  which  can  be  said  to  maintain  an 
animal  without  loss  of  vitality.  When  the  minimal  amount 
necessary  for  the  prevention  of  loss  of  weight  is  approached, 
the  life  of  the  animal  is  jeopardized  if  the  diet  is  persisted  in." 
They  also  find  that  "  the  animal  can  tolerate  being  Hmited  to 
a  very  low  intake  of  either  the  dietary  A  or  B  much  better  with 
an  otherwise  excellent  diet  than  when  it  is  less  well  constituted," 
and  also  that  "it  is  better  to  have  a  Hberal  supply  of  one 
and  a  minimal  supply  of  the  other  of  the  A  and  B  than  the 
minimal  allowance  of  both."  The  presence  of  sufficient  quan- 
tities of  these  substances  is  insured  by  making  prominent  in 
the  diet  the  types  of  foods  rich  in  them.  These  are  chiefly: 
milk  and  its  products,  eggs,  vegetables,  fruits,  and  the  outer 
portions  of  the  cereal  grains  —  all  foods  which  it  is  wise  to 
make  prominent  in  the  diet  for  other  reasons  as  well.  It 
will  be  remembered  that  "  fat  soluble  A  "  and  "  water  soluble 
B  "  may  or  may  not  occur  abundantly  in  the  same  articles  of 
food.  Milk,  eggs,  and  green  vegetables  appear  to  be  rich  in 
both;  butter  in  "  fat  soluble  A  "  and  whole  grains  in  "  water 
soluble  B."  Thus  either  milk  or  eggs  alone,  or  both  butter 
and  whole  grain  products,  would  provide  the  two  kinds  of  un- 
identified essentials.  When  both  economy  and  efficiency  are 
considered,  it  appears  that  milk  and  vegetables  are  especially 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      385 

worthy  of  a  more  prominent  place  in  the  diet  than  is  commonly 
given  them  in  present  American  practice. 

Limitations  of  Dietary  Standards.  —  At  the  risk  of  repetition 
let  it  be  clear  that  too  much  weight  must  not  be  attached  to  any 
of  the  so-called  dietary  standards,  i.e.  to  any  attempt  to  state 
the  requisites  of  an  adequate  diet  in  terms  of  quantities  of  cer- 
tain nutrients.  As  Atwater  sought  strongly  to  emphasize,  a 
dietary  standard  at  best  is  "  only  an  indication,  not  a  rule." 
Some  of  those  who  have  been  most  active  in  recent  investiga- 
tion are  most  emphatic  in  warning  against  the  expectation  that 
dietary  standards  can  be  made  to  embrace  all  the  qualities 
which  a  diet  must  have  in  order  to  be  permanently  adequate. 
Thus  Hart,  McCoUum,  Steenbock,  and  Humphrey  in  a  very 
recent  article  *  say : 

"  With  this  recognition  of  all  the  normal  factors  for  adequate 
nutrition  there  must  not  simultaneously  arise  a  desire  for  a 
mathematical  expression  of  these  factors  in  feeding  standards. 
It  is  doubtful  if  this  can  ever  be  done,  at  least  for  certain  of  them. 
For  example,  the  r61e  of  the  mineral  nutrients  is  so  varied,  in- 
cluding such  widely  separate  functions  as  construction  and  con- 
trol through  antagonism,  as  to  make  it  seem  futile  to  attempt 
an  expression  of  absolute  requirements  when  natural  foods, 
with  their  diversity  of  mineral  content,  are  involved.  Even 
the  recognition  of  differences  in  the  quality  of  proteins  and  their 
relation  to  nutrition  will  make  it  more  difficult  to  continue  ex- 
pressing protein  requirements  in  exact  quantities  than  before 
the  development  of  such  knowledge ;  and  what  can  be  said  of 
the  quantitative  requirements  of  fat  soluble  A  and  water  sol- 
uble B  and  their  supply  in  feeding  materials?  We  need  more 
effort  placed  on  the  accumulation  of  information  on  the  phys- 
iological behavior  of  feeding  stuffs  than  on  the  attempts  to 
bring  out  new  mathematical  expressions  of  feeding  standards." 

*  Proceedings  of  the  National  Academy  of  Sciences,  Vol.  3,  page  374  (May, 

1917). 

20 


386  CHEMISTRY  OF  FOOD  AND  NUTRITION 

The  Economic  Use  of  Food 

True  economy  in  the  use  of  food  must  be  physiological  as  well 
as  pecuniary  economy.  The  diet  must  supply  amply  all  the 
requirements  of  nutrition  (not  merely  the  appetite  nor  the  need 
for  energy  and  protein)  and  this  must  be  accompHshed  without 
the  expenditure  of  too  large  a  proportion  of  the  income.  The 
majority  of  famiUes  in  the  United  States  have  had  in  recent 
normal  times  incomes  of  less  than  $800  per  year,  of  which  not 
over  45  per  cent  can  be  spent  for  food  if  other  Hving  conditions 
are  to  be  at  all  satisfactory.  This  implies  an  allowance  of  ap- 
proximately one  dollar  per  day  for  food  for  the  ''  normal  "  family 
of  five,*  or  20  cents  per  capita  per  day. 

If  this  be  taken  as  approximating  the  average  expenditure 
in  normal  years,t  it  would  follow  that  the  sum  annually  spent 
for  food  in  the  United  States  is  in  the  neighborhood  of 
$7,000,000,000.  From  such  statistical  estimates  of  the  value 
of  the  different  food  industries  as  the  writer  has  been  able  to 
find  it  would  appear  that  this  is  distributed  somewhat  as  follows : 

Meats,  poultry,  fish,  and 

shellfish     .     .     .     .     .  about  $2,800,000,000  —  or  about  40  per  cent. 

Eggs about     $400,000,000  —  or  about    6  per  cent. 

Milk about     $500,000,000  —  or  about    7  per  cent. 

Cheese about       $50,000,000  —  or  less  than  i  per  cent. 

Butter  and  other  fats     .  about     $500,000,000  —  or  about    7  per  cent. 

Grain  products      .     .     .  about  $1,000,000,000  —  or  about  14  per  cent. 

Sugar,  molasses,  etc.       .  about     $500,000,000  —  or  about    7  per  cent. 

Vegetables about     $500,000,000  —  or  about    7  per  cent. 

Fruits about     $300,000,000  —  or  about    4  per  cent. 

Nuts  t about       $50,000,000  —  or  less  than  i  per  cent. 

Miscellaneous,  §  by  difference  about  6  to  7  per  cent. 

*  If  the  family  of  five  be  reckoned  as  equivalent  in  food  requirements  to  3.7 
men,  the  amount  here  suggested  as  available  for  food  would  correspond  to  27  cents 
"per  man  per  day"  or  "per  unit." 

t  No  attempt  is  made  in  this  chapter  to  quote  the  fluctuations  of  prices  under 
war  conditions.  The  economic  relationships  here  discussed  will  be  found  to  be  but 
little  disturbed  by  a  general  raising  or  lowering  of  the  level  of  prices. 

J  This  estimate  doubtless  includes  considerable  quantities  of  nuts  not  used  as 
such  for  human  food  but  pressed  for  oil  and  the  residue  fed  to  farm  animals. 

§  Including  beverages,  condiments,  and  minor  unclassified  food  materials. 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD     387 

Any  such  estimates  as  these  can  be  no  more  than  rough  ap- 
proximations since  they  depend  upon  data  which  are  by  no  means 
complete  and  accurate  for  the  year  in  which  gathered  and  are 
subject  to  fluctuation  from  year  to  year.  It  also  appears  im- 
possible to  avoid  arbitrary  assumptions  regarding  the  relations 
of  wholesale  and  retail  values.  They  are  intended,  therefore, 
only  to  indicate  in  the  most  general  way  the  relative  prominence 
of  expenditure  for  the  different  types  of  food  materials  as  judged 
from  the  statistics  of  the  food  industries. 

Another  statistical  estimate  may  be  obtained  from  the  data 
published  by  the  U.  S.  Bureau  of  Labor  Statistics,  who  report 
that  of  the  total  value  of  food  consumed  in  2567  workingmen's 
families  the  distribution  of  expenditure  was  as  follows : 


Meat,  poultry,  and  fish  .     .     . 

Eggs        

MUk 

Cheese 

Butter  and  lard 

Grain  products 

Sugar  and  molasses    .     .     .     . 

Vegetables 

Fruit 

Other  food  and  food  adjuncts 


Per  Cent  of  Total 
Cost  of   Food 


33-80 

5-14 
6.52 
0.80 
11.66 
9-57* 
5-34 
9.72 
5.0s 
7.50 


These  averages  are  based  upon  data  which  were  apparently 
obtained,  for  the  most  part  at  least,  by  simply  asking  questions 
of  the  housewife  regarding  the  kinds,  amounts,  and  costs  of  her 
food  purchases  and  relying  upon  her  memory  for  the  facts. 
The  probable  errors  in  data  for  individual  families  would  thus 
be  large,  but  the  great  number  of  families  included  in  the  inquiry 
would  tend  to  minimize  the  errors  in  the  final  average. 

*  Low  partly  because  of  purchase  of  flour  rather  than  bread,  partly  because  oat- 
meal, etc.,  were  often  not  reported  under  this  head  but  under  "other  foods." 


388 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


A  different  kind  of  data  bearing  on  this  same  problem  is  found 
in  the  dietary  studies  made  under  the  auspices  of  the  United 
States  Department  of  Agriculture  or  of  the  New  York  Associa- 
tion for  Improving  the  Condition  of  the  Poor.  These  dietary 
studies  are  accurate  records  of  the  kinds  and  amounts  of  foods 
consumed  by  given  groups  of  people  during  a  period  of  a  week 
or  more.  From  such  studies,  chiefly  of  family  groups,  208 
have  been  taken  as  presumably  representative  of  American 
food  habits  generally,  and  the  cost  of  these  dietaries  has  been 
studied  with  reference  to  the  distribution  of  expenditure  under 
headings  corresponding  to  those  used  in  the  case  of  the  above 
statistical  estimates  with  the  following  results: 


Per  Cent  of 

Total  Cost 

or  Food 


Meats  and  fish  (including  poultry  and  shellfish  if  used) 

Eggs    "... 

Milk  (including  cream  if  used) 

Cheese 

Butter  and  other  fats 

Grain  products 

Sugar,  molasses,  etc 

Vegetables 

Fruit  (and  nuts  if  used)       

Miscellaneous  * 


34-3 
5.7 
9.6 
i.o 
8.6 

17.4 
4-5 

lO.I 

5-0 
3.8 


Of  the  dietaries  included  in  the  above  average,  92  constituted 
a  series  observed  during  1914-1915  in  connection  with  the  food 
investigations  of  the  New  York  Association  for  Improving  the 
Condition  of  the  Poor.  These  studies  were  not  entirely  confined 
to  New  York  City  nor  to  families  of  low  incomes.  The  cost 
of  food  per  man  per  day  ranged  from  12  to  76,  averaging  34 
cents.     The  median  cost  was  31.5  cents  per  man  per  day.     In 


*  Tea,  coflfee,  and  other  food  adjuncts  were  usually  but  not  always  reported  under 
this  heading.    The  reported  average  is  therefore  somewhat  below  the  truth. 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      389 

one  fourth  of  the  famiHes  the  cost  was  below  25  cents ;  in  one 
fourth  it  was  above  40  cents ;  in  one  half  it  was  between  25  and 
40  cents  per  man  per  day. 

The  average  distribution  of  expenditure  in  these  92  famihes 
was  as  follows : 


Per  Cent  of 

Total  Cost 

OF  Food 


Meat  and  fish  (including  poultry  and  shellfish  when 
used) 

Eggs 

Milk  (and  cream  if  used) 

Cheese 

Butter  and  other  fats 

Grain  products 

Sugar,  molasses,  etc 

Vegetables 

Fruit 

Nuts 

Miscellaneous  (chiefly  beverages,  condiments,  and 
other  food  adjuncts) 


33.19 
5-55 
9.08 

1. 13 
8.14 

17.85 
3.80 
9.12 
6.03 
0.35 

5.76 


When  these  92  studies  were  grouped  according  to  the  amount 
spent  per  man  per  day  for  food,  it  was  apparent  that  as  the  scale 
of  expenditure  became  more  liberal  a  larger  proportion  of  the 
money  was  spent  for  butter  and  fruit  and  a  smaller  proportion 
for  breadstuffs.  The  distribution  of  expenditure  among  other 
types  of  food  was,  however,  very  similar  in  the  dietaries  of  low, 
medium,  and  high  cost. 

Each  of  the  three  kinds  of  evidence  used  in  arriving  at  the 
above  estimates  of  distribution  of  expenditure  for  food  may 
readily  be  criticized  as  inaccurate  or  inconclusive  or  both.  Yet 
the  trend  of  the  data  derived  from  the  different  kinds  of  evi- 
dence is  so  consisftnt  that  it  can  hardly  be  devoid  of  signifi- 
cance. It  can  scarcely  be  doubted  that  of  the  money  devoted 
to  the  purchase  of  food  the  average  American  family  spends 


390  CHEMISTRY  OF  FOOD  AND  NUTRITION 

from  30  to  40  per  cent  for  meats  and  fish  (including  poultry 
and  shellfish  when  used),  about  5  or  6  per  cent  for  eggs,  about 
7  to  10  per  cent  for  milk,  from  7  to  12  per  cent  for  butter  and 
other  fats,  from  10  to  20  per  cent  for  bread  and  other  cereal 
and  bakery  products,  3  to  7  per  cent  for  sugar  and  other  sweets, 
7  to  10  per  cent  for  vegetables,  2  to  8  per  cent  for  fruit,  and  less 
than  2  per  cent  for  cheese  and  nuts.  At  the  same  time  it  is 
plain  that  such  a  food  budget,  however  prevalent,  need  not  be 
regarded  as  fixed.  Many  people  occasionally,  and  some  habit- 
ually, put  the  last  and  smallest  of  the  items  just  mentioned  in 
the  place  of  the  first  and  largest  by  using  cheese  or  nuts  as  so- 
called  "  meat  substitute,"  more  properly  as  an  alternative  to 
meat,  —  a  custom  which  on  the  whole  appears  to  be  growing. 
The  place  of  each  type  of  food  in  the  diet  has  been  discussed 
in  a  general  way  elsewhere  *  and  space  does  not  permit  us  to 
go  over  the  same  ground  here. 

That  the  writer  does  not  regard  the  usual  distribution  of 
expenditure  for  food  in  American  famiHes  as  being  either  inevi- 
table or  ideal  may  be  indicated  by  the  fact  that  in  his  own  house- 
hold, consisting  of  three  adults  and  four  growing  children,  the 
distribution  of  money  expended  for  food  is  about  as  follows : 


Per  Cent  of 

Total  Cost 

OF  Food 


Meats,  poultry,  and  fish 

Eggs 

Milk 

Cheese 

Butter  and  other  fats 

Bread,  cereals,  and  other  gr^in  products 
Sugar,  molasses,  and  syrups   .... 
Vegetables  and  fruits 


10-15 
5-7 

25-30 
2-3 

10-12 

12-15 
about  3 

15-18 


♦Sherman,  Food  Products,  pages  74-81,  108-111,  139-141,  212-216,  288-295, 
346-351,  357,  388-393,  440-444- 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      391 

Just  what  prominence  should  be  given  to  each  type  of  food 
in  the  provisioning  of  a  given  family  or  community  is  a  problem 
calling  for  consideration  of  many  factors.  One  important  fea- 
ture of  the  problem  is  to  ascertain  how  the  normal  distribution 
of  expenditure  among  the  various  types  of  food  materials  affects 
the  relative  proportions  of  nutrients  in  the  resulting  mixed  diet. 
The  accompanying  table  permits  a  comparison  between  the 
expenditures  for  the  different  types  of  food  and  the  returns 
from  each  in  terms  of  energy,  protein,  calcium,  phosphorus,  and 
iron  in  the  case  of  the  series  of  92  family  dietaries  described  on 
page  389.  In  individual  dietaries  the  returns  will  naturally 
vary  according  as  an  economical  or  an  expensive  food  of  its  kind 
is  chosen,  but  in  the  average  of  92  different  dietaries,  each  of  a 
week's  duration,  the  danger  of  error  due  to  such  individual 
variations  is  minimized. 


Each  Type  of  Food  in  Percentage  of  Total  (Average  of  92  Dietaries) 


Meats  and  fish  .     . 

Eggs 

Milk*  .  .  .  . 
Cheese  .... 
Butter    and    other 

fats 

Grain  products 
Sugar  and  molasses 
Vegetables     .     .     . 

Fruits 

Nuts 

Miscellaneous     .     . 


Cost         Calories       Protein       Calcium    Phosphorus      Iron 


33-19 

5-55 
9.08 

1. 13 

8.14 
17.85 
3.80 
9.12 
6.03 

0.35 
S.76 


16.54 

1-75 
8.11 
0.94 

10.29 

37.79 
10.78 

9.03 
3.87 
0.27 
0.65 


36.29 

4.49 

10.13 

2.08 

0.28 
35.86 
0.07 
8.91 
1.08 
0.22 
0.59 


3.68 

3.25 

50.19 

7.28 

0,67 

15-31 
0.69 

13-25 
4.66 
0.14 
0.88 


26.70 
4.00 

18.52 
2.96 

0.33 
28.85 
0.06 
14.65 
2.41 
0.26 
1.26 


31-43 
6.18 
4.72 
0.5s 

0.39 

24-95 
0.20 

26.22 
4.09 
0.18 
1.09 


If  we  compare  the  cost  of  each  type  of  food  with  the  energy  and  individual 
nutrients  which  it  furnishes,  we  find  that  because  of  the  differing  prominence 
of  the  several  factors  of  food  value  in  the  various  types  of  food  it  is  often 
difficult  to  decide  which  expenditures  were  more  economical.  Thus  in  the 
averages  just  given  rritat  and  fish  cost  one  third  of  the  total  expenditure 

*  Cream,  in  those  cases  in  which  it  was  purchased,  is  here  included  with  milk. 
The  amount  of  cream  was  small,  if  any. 


392 


CHEMISTRY  OF  FOOD  AND  NUTRITION 


for  food  and  furnished  about  one  third  of  the  protein,  phosphorus,  and  iron 
but  only  one  sixth  of  the  energy  and  only  about  one  thirtieth  of  the  calcium. 
Eggs  furnished  protein,  phosphorus,  and  iron  about  in  proportion  to  their 
cost,  but  less  calcium  and  much  less  than  a  proportionate  amount  of  energy. 
Milk  furnished  calories  and  protein  about  in  proportion  to  cost,  twice  as 
much  phosphorus,  and  five  times  as  much  calcium  in  proportion,  but  only 
half  as  much  iron. 

By  adopting  the  principle  of  a  score  card  and  assigning  weights  to  the 
different  factors  of  food  value,  it  becomes  feasible  to  compute  a  "com- 
posite valuation"  or  "score"  for  each  food  or  group  of  foods  which  may 
then  be  compared  with  its  cost.  Since  the  most  frequent  deficiency  in 
American  dietaries  is  inadequacy  of  total  food  or  energy  value  and  most 
dietaries  actually  observed  are  of  such  composition  as  would  furnish  enough 
of  each  essential  element  if  the  total  amount  of  food  eaten  were  sufficient 
to  provide  a  liberal  energy  supply,  it  seems  reasonable  to  assign  to  the  energy 
value  of  a  diet  a  weight  of  about  half  of  its  composite  valuation.  It  also 
seems  reasonable  to  assign  the  remaining  "points"  equally  to  protein, 
calcium,  phosphorus,  and  iron.* 

If  then  we  give  to  energy  a  weight  of  60  on  a  scale  of  100  and  to  protein, 
calcium,  phosphorus,  and  iron  each  a  weight  of  10,  or  to  energy  40  and  to 
protein,  calcium,  phosphorus,  and  iron  each  15,  we  obtain  from  the  data 
of  the  table  above  the  "score  values"  or  "composite  valuations"  under 
the  designations  "I"  and  "II"  respectively  in  the  table  which  follows : 


Meats  and  fish 

Eggs 

Milk  (and  cream) 
Cheese      .     .     .     .     , 
Butter  and  other  fats 
Grain  products 
Sugar  and  molasses 
Vegetables     .     .     .     , 

Fruit , 

Nuts 

Miscellaneous    .     . 


"  Score  Value  "  or 

Cost 

"  Composite  Valuation  " 

I 

II 

33.19 

19.73 

21.33 

S-5S 

2.84 

3.39 

9.08 

13.22 

15.78 

1.13 

1.85 

2.30 

8.14 

6.34 

4.37 

17.85 

33.17 

30.85 

3.80 

6.57 

4-47 

9.12 

11.72 

13.07 

6.03 

3.5s 

3.38 

0.3s 

0.24 

0.23 

5.76 

0.77 

0.83 

*  In  reality  this  amounts  to  giving  a  higher  valuation  to  the  protein  since  this 
is  counted  both  as  protein  and  as  a  part  of  the  energy  supply  as  well. 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      393 

By  comparing  the  composite  valuation  with  the  cost  it  will  be  seen  that 
if  either  of  these  methods  of  estimating  comparative  values  is  at  all  valid, 
the  money  spent  in  these  92  families  for  milk  and  cheese,  grain  products, 
and  vegetables  brought  a  better  relative  return  in  food  value  and  was  there- 
fore in  this  sense  better  invested  than  the  money  spent  for  meats  and  fish, 
eggs,  and  fruit. 

In  making  any  such  comparison  it  must  be  kept  prominently  in  mind : 
(i)  that  the  weights  assigned  to  the  different  factors  of  food  value  must 
necessarily  be  more  or  less  arbitrarily  chosen  so  that  the  resulting  "com- 
posite valuations"  or  "food  values"  rest  partly  on  facts  and  partly  on 
assumptions;  (2)  that  not  all  the  important  factors  of  food  value  are  taken 
into  account  in  these  valuations,  "vitamine  values"  for  instance  being 
wholly  omitted  from  the  calculation  because  as  yet  we  have  not  the  data 
necessary  to  permit  us  to  give  them  numerical  expression.  It  is  quite 
possible  that  when  it  becomes  feasible  to  state  the  vitamine  values  in  numer- 
ical terms  and  give  them  due  weight  in  the  composite  valuation,  the  expendi- 
tures for  eggs  and  butter  may  appear  more  economical  than  is  indicated 
by  the  above  table.  Any  comparisons  based  on  the  use  of  such  arbitrary 
weights  or  valuations  as  can  at  present  be  assigned  must  therefore  be  used 
with  much  discretion  if  misconceptions  are  to  be  avoided;  but  if  so  used 
they  may  be  found  serviceable  in  guiding  the  economical  choice  of  food  and 
to  some  extent  in  teaching  relative  food  values. 

Individual  articles  of  food  may  be  given  "  score  values  "  or  "  composite 
valuations  "  in  a  similar  manner.  Thus  if  100  Calories  be  given  a  value  of 
40  on  the  scale  of  100,  and  such  quantities  of  protein,  phosphorus,  calcium 
and  iron  as  should  accompany  100  Calories  in  an  adequate  economical  diet 
be  given  a  value  of  15  each,  the  score  for  almonds  might  be  ascertained 
as  follows : 

To  every  100  Calories  of  almonds  there  are  3.23  grams  of  protein,  0.071 
gram  of  phosphorus,  0.039  gram  of  calcium,  and  0.0006  gram  of  iron.  If 
we  accept  the  allowance*  of  75  grams  of  protein,  1.44  grams  of  phosphorus, 
0.68  gram  of  calcium,  and  15  milligrams  of  iron  per  man  per  day,  then  to 
every  100  Calories  of  the  3000  ordinarily  taken  as  the  requirement  of  a  man 
at  ordinary  labor,  there  should  be  2.5  grams  of  protein,  0.048  gram  of  phos- 
phorus, 0.023  gram  of  calcium,  and  0.0005  gram  of  iron.  Then  to  every  100 
Calories  of  almonds  there  is  1.3  (3.23  divided  by  2.5)  times  the  amount  of 
protein  required  to  "  balance  "  the  energy  value ;  1.48  times  the  amount  of 
phosphorus,  1.61  times^e  amount  of  calcium,  and  1.2  times  the  amount  of 
iron.  Scoring  these  as  indicated  above,  we  have  the  score  value  for  almonds 
as  follows : 

*  See  page  383. 


394 


CHEMISTRY  OF  FOOD  AND   NUTRITION 


Assumed  Values 


Score 
Points 


Calories  (loo) 40 

Protein 1.3    X  15 

Phosphorus 1.48  X  15 

Calcium i. 61  X  15 

Iron        1.20  X  15 


40 

19.S 
22.2 
24.2 
18.0 
123.9 


Since  a  pound  of  almonds  contains  16.14  loo-Calorie  portions,  then  a 
pound  of  almonds  has  a  score  value  of  2000  (123.9  multiplied  by  16.14). 
The  following  table  gives  the  score  value  of  common  typical  foods  : 

Approximate   Score   Value   (Composite   Valuation)   per   Pound   of 
Some  Common  Typical  Foods  as  Purchased 


Meat  —  Beef,  sirloin 

Bacon 

Eggs 

Cheese  — 

Cottage       .     .     .     . 

Hard  American    .     . 
Milk  —  Condensed 
sweetened    .     .     . 
unsweetened     .     . 

Skimmed    .     .     .     . 

Whole 

Butter 

Cream— 18. 5%  fat     . 

40%  fat      .     .     .     . 

Lard 

Olive  oil 

Sugar    

Grain  Products  —  .     . 

Bread,  entire  wheat 

Bread,  white 


1290 
1770 
1092 

1287 
4460 

2000 

1556 

500 

600 

2320 

860 

1350 
2450 
2450 
1090 

1250 
1098 


II" 


1460 
1460 
1341 

1688 
5690 


1955 

670 

700 

1750 

860 

1150 

1650 

1650 

725 

1320 
1060 


Grain  Products  (Con.) 
Bread,  rye  .  . 
Corn  meal  .  . 
Crackers  .  . 
Corn  flakes 
Farina  .  .  . 
Flour,  graham 
Flour,  rye  .  . 
Flour,  white  . 
Hominy  .  . 
Macaroni  .  . 
Oatmeal  .  . 
Rice,  white 

Vegetables  — 
Asparagus,  fresh 
Beans,  dry,  white 
Beans,  dry,  Limas 
Beans,  fresh  Limas 
Beans,  string  .     . 
Beets     .... 


1125 
1444 

1579 
1270 
1418 
2000 
1502 
1372 
1301 
1502 
2245 
1289 

279 
2750 
2380 
3(>3 
374 
246 


11^ 


mi 
1360 

1433 
1090 
1308 
2150 
1459 
1257 
1147 
1444 
2465 
1139 

368 

3350 

2780 

420 

472 

286 


*The  two  sets  of  arbitrary  score  values  correspond  to  the  two  systems  of 
"  weights  "  or  "  points  "  explained  above.  The  score  value  will  vary  slightly  with 
the  data  of  the  particular  analysis  and  should  perhaps  be  expressed  only  in  round 
numbers, 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      395 

Approximate   Score   Value   (Composite   Valuation)  per  Pound   of 
Some  Common  Typical  Foods  as  Purchased  —  Continued 


Vegetables  (Con.) 
Cabbage    . 
Carrots 
Cauliflower 
Celery    .     . 
Corn,  canned 
Cucumbers 
Lentils    .     . 
Lettuce  .     . 
Onions    .     . 
Peas,  dry    . 
Peas,  fresh  . 
Parsnips 
Potatoes,  sweet 
Potatoes,  white 
Radishes     .     , 
Spinach  .     ,     . 
Squash   .     .     . 
Tomatoes    .     . 
Turnips       .     . 

Fruit  — 
Apples,  fresh   . 
Apples,  dry     . 


I* 

II* 

^85 

367 

278 

338 

487 

640 

256 

350 

497 

523 

125 

153 

2834 

3464 

280 

380 

280 

330 

2510 

2960 

400 

475 

349 

405 

399 

374 

377 

414 

161 

195 

630 

890 

130 

144 

162 

192 

246 

307 

175 

156 

1075 

955 

Fruit  (Con.) 

Bananas  .     . 

Dates       .     . 

Grapefruit    . 

Grapes     . 

Lemons    .     . 

Olives 

Oranges   . 

Peaches,  fresh 

Pears  .     .     . 

Pineapple 

Plums      .     . 

Prunes     .     . 

Raisins    .     . 
Nuts  — 

Almonds*     . 

Cocoa 

Filberts*       . 

Peanuts* 

Pecans*  .     . 

Walnuts* 


254 

1298 

167 

286 

199 

1000 

209 

169 

236 

234 

345 

1 144 

1500 

1900 
2900 
1676 
2010 
1556 
730 


11=' 


236 

1240 
169 
266 
228 

1000 
228 
177 
228 
253 
337 

113s 

1550 

2000 
3231 
1752 
2078 
1440 
670 


By  dividing  the  "Score  Value"  of  a  pound  of  any  food  by  the  price  in 
cents  per  pound  one  finds  the  number  of  score  units  or  points  of  food  value 
obtained  for  each  cent,  and  a  comparison  of  different  foods  on  this  basis 
gives  some  indication  of  their  relative  economy,  if  the  limitations  of  such 
comparisons  are  held  strictly  in  mind.  Among  these  limitations  may  be 
mentioned  (i)  the  fact  already  noted  that  such  valuations  necessarily  in- 
volve the  arbitrary  assignment  of  weights  to  the  different  factors  or  phases 
of  food  value  so  that  facts  and  assumptions  are  inseparably  combined  in 
the  final  results  notwithstanding  the  numerical  form  in  which  these  are 
expressed;  (2)  the  further  tacit  assumption  that  a  given  amount  of  protein, 
of  phosphorus,  of  calcium,  or  of  iron  is  of  the  same  value  in  whatever  food 


*  With  sbeJl 


396  CHEMISTRY  OF  FOOD  AND  NUTRITION 

found,  which  is  certainly  not  true  in  detail  and  may  be  very  far  from  true 
in  many  cases ;  (3)  that  any  such  attempt  to  reduce  the  values  of  different 
types  of  food  to  a  single  basis  for  comparison  necessarily  tends  to  obscure 
those  differences  of  composition  and  character  between  the  different  types 
of  food,  which  must  be  kept  in  mind  in  order  that  one  may  give  each  type 
of  food  its  proper  place  and  thus  secure  a  well-balanced  dietary. 

Let  us  return  then  to  the  consideration  of  the  average  data 
of  the  92  dietaries  as  given  in  the  table  on  page  391. 

The  average  food  value  of  these  92  dietaries  calculated  per 
man  per  day  was  as  follows : 

Energy 2928  Calories 

Protein loi  Grams 

Calcium 0.72      Gram  (i. 01  Grams  CaO) 

Phosphorus ,  1.52      Grams  (3.48  Grams  P2O5) 

Iron 0.0166  Gram 

Comparing  these  averages  with  the  amounts  actually  required 
for  normal  nutrition  (page  383)  it  will  be  seen  that  the  freely 
chosen  dietaries  contained  a  liberal  surplus  of  protein  and  a  fair 
supply  of  phosphorus  and  iron  but  scarcely  more  than  is  ac- 
tually necessary  of  calories  or  of  calcium.  Correspondingly  we 
find  that  the  number  of  individual  family  dietaries  actually 
deficient  in  calcium  and  in  total  food  value  (calories)  is  high 
enough  to  cause  serious  concern,  while  the  cases  of  deficiency 
of  phosphorus  or  iron  were  considerably  less  frequent  and  there 
were  few  if  any  cases  showing  an  actual  deficiency  of  protein. 

This  suggests  that  there  would  be  true  economy  in  a  some- 
what different  distribution  of  expenditure  by  which  less  should 
be  spent  for  expensive  high  protein  food,  unless  it  is  also  rich 
in  calcium  or  furnishes  a  high  energy  value  in  proportion  to  its 
cost,  while  more  prominence  should  be  given  to  those  foods 
which  are  rich  in  calcium  or  are  advantageous  sources  of  energy 
without  being  conspicuously  poor  in  phosphorus  and  iron.  In 
general  this  would  mean  somewhat  less  meat  and  somewhat 
more  of  milk  and  vegetables,  of  the  cheaper  sorts  of  fruit,  and 
of  bread  or  other  grain  products  in  the  diet. 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD      397 

Breadstuffs  and  other  staple  grain  products  always  give  a  high 
energy  return  as  compared  with  their  cost,  and  usually  also  a 
high  return  in  protein  and  ash  constituents,  the  latter,  however, 
depending  largely  upon  whether  "  whole  grain  "  or  highly 
milled  products  are  used.  In  general  the  more  economical 
the  dietary  must  be  the  higher  should  be  the  proportion  of  ex- 
penditure for  bread  (or  other  grain  products)  and  the  more 
restricted  the  dietary  the  more  desirable  it  becomes  to  use 
"  whole  grain  "  rather  than  highly  milled  products. 

Meats  give  usually,  as  compared  with  their  cost,  a  fair  return 
in  protein,  phosphorus,  and  iron,  a  low  return  in  energy,  and 
an  extremely  low  return  in  calcium.  Milk,  on  the  other  hand,  is 
very  rich  in  calcium  and  furnishes  in  proportion  to  its  cost  more 
energy  and  phosphorus  than  does  meat  of  average  fatness,  and 
proteins  and  iron  of  at  least  equal  value  if  not  of  equal  amount. 
Milk  also  excels  other  foods  in  respect  to  the  advantageous 
quantitative  relationships  of  its  ash  constituents  and  is  probably 
the  best  possible  source  of  the  growth-promoting  substances 
needed  by  all  young  mammals.  The  well-known  dietary  rule  of 
"  a  quart  of  milk  a  day  for  every  child,"  already  amply  justified 
by  practical  results,  has  received  additional  support  from  several 
angles  through  the  recent  advances  in  our  knowledge  of  the 
chemistry  of  nutrition. 

Armsby  estimates  that  of  the  energy  value  of  grain  about 
18  per  cent  is  recovered  for  human  consumption  in  milk  and 
only  about  3.5  per  cent  in  beef. 

While  milk  is  somewhat  poor  in  iron,  that  which  it  contains 
is  exceptionally  efl&cient  in  nutrition.  Moreover,  the  supply 
of  this  element  may  readily  be  safeguarded  either  by  the  use  of 
whole  grain  products  or  by  increasing  the  proportion  of  fruits  and 
vegetables  in  the  diet.  It  will  be  recalled  from  what  has  been 
said  in  earlier  chajJters  that  an  abundance  of  fruits  and  vege- 
tables in  the  diet  is  also  advantageous  in  other  important  ways. 
Vegetables  and  some  fruits,  economically  selected,  bring  a  good 


398  CHEMISTRY  OF  FOOD  AND  NUTRITION 

return  in  nutrients  for  the  money  expended  and  their  Hberal 
use  adds  greatly  to  both  the  attractiveness  and  the  wholesome- 
ness  of  the  diet. 

It  therefore  seems  advisable  to  spend  at  least  as  much  for 
fruit  and  vegetables  as  for  meat  and  fish ;  also  to  spend  at  least 
as  much  for  milk  as  for  meat  (or  for  milk  and  cheese  as  for  meat 
and  fish). 

At  ordinary  prices  eggs  are  about  as  cheap  a  food  as  meat, 
and  cheese  (like  milk)  is  much  cheaper  than  meat  in  proportion 
to  its  food  value.  Eggs  and  cheese  can  therefore  be  substi- 
tuted for  meat  to  any  extent  desired  in  the  individual  dietary 
without  detriment  to  its  nutritive  value  and  usually  with  good 
economy. 

General  adoption  of  a  dietary  such  as  we  now  believe  to  be 
best  would  call  for  more  milk  and  perhaps  more  vegetables  and 
fruit  than  now  come  to  our  city  markets;  but  more  of  these 
foods  will  be  produced  and  marketed  as  the  demand  for  them 
increases.  Moreover  an  increased  demand  for  these  foods  and 
a  correspondingly  decreased  (per  capita)  demand  for  meat,  so 
far  from  causing  any  serious  "  dislocation  of  industry,"  will 
help  to  facilitate  natural  evolution  of  American  agriculture. 
With  increasing  population  on  stationary  area  farming  neces- 
sarily becomes  more  intensive.  Beef  is  produced  less  by  the 
grazing  of  cattle  on  free  ranges  of  unbroken  prairie  and  more 
by  the  feeding  of  grain  and  other  cultivated  crops.  For  a  given 
amount  of  food  consumed  a  dairy  herd  yields  a  product  of  greater 
food  value  than  does  a  herd  of  beef  animals.  An  increasing 
ratio  of  milch  cows  to  beef  cattle  is  naturally  to  be  expected 
with  the  development  of  a  more  intensive  agriculture  and  will 
be  to  the  advantage  of  producer  and  consumer  alike.  In  re- 
gions adapted  to  dairy  farming  but  too  remote  from  large  mar- 
kets to  ship  in  the  fresh  state  we  may  anticipate  an  increasing 
production  of  condensed  and  dried  milk  and  of  butter  and  cheese. 
An  increased  production  of  fruit  and  vegetables  should  also  be 


DIETARY  STANDARDS  AND   ECONOMIC  USE  OF  FOOD      399 

a  natural  result  of  a  more  stable  and  intensive  agriculture.  At 
the  same  time  the  concentration  of  population  in  large  cities 
increases  the  expense  of  transportation  and  makes  the  cost  of 
retail  distribution  a  serious  item,  especially  in  the  case  of  bulky- 
products  with  a  relatively  low  value  per  pound.  Cabbage, 
potatoes,  and  root  crops  can  be  produced  at  a  low  cost  per  ton, 
but  the  percentage  of  the  cost  of  production  which  must  be 
added  when  they  are  distributed  through  modern  retail  agencies 
tends  constantly  to  increase. 

The  more  highly  perishable  fruits  and  vegetables  having  a 
higher  cost  per  pound  or  ton  are  now  successfully  transported 
in  transcontinental  carload  shipments.  Precooling  and  low- 
ered temperatures  in  refrigerator  cars,  secured  by  the  use  of 
salt  with  ice,  promise  to  reduce  still  further  the  losses  incident 
to  their  transportation. 

Cold  storage  tends  to  equalize  prices  throughout  the  season 
on  such  perishable  foods  as  butter,  cheese,  and  eggs,  and  secures 
a  supply  of  other  fresh  foods  such  as  apples,  of  good  quality, 
throughout  almost  the  entire  year.  With  the  perfection  of 
facilities  for  more  rapid  distribution  in  cities  after  removal  from 
freezing  temperatures  the  number  and  quantity  of  vegetables 
and  fruits  so  preserved  should  increase  greatly.  The  canning 
industry  has  already  developed  to  enormous  proportions  and 
it  seems  likely  that  drying  processes  will  be  applied  to  a  con- 
stantly increasing  number  of  the  more  bulky  vegetables. 

The  physical  and  economic  wastes  in  marketing  are  being 
reduced  by  various  agencies  in  the  United  States  Department  of 
Agriculture,  now  largely  consolidated  in  the  Bureau  of  Markets, 
and  in  general  the  supply  may  be  trusted  to  keep  pace  with  the 
demand  in  the  gradual  shifting  of  emphasis  from  meat  toward 
dairy  products,  vegetables,  and  fruit,  which  seems  to  be  clearly 
desirable  both  in  \iew  of  our  present  knowledge  of  nutrition, 
and  in  the  light  of  our  agricultural  situation. 

The  broader  and  more  accurate  conception  of  food  values 


400  CHEIVIISTRY  OF  FOOD  AND  NUTRITION 

which  is  made  possible  by  the  recent  advances  in  the  chemistry 
of  food  and  nutrition  will  guide  the  judgment  both  as  to  the 
proper  emphasis  to  be  placed  upon  each  type  of  foods  in  the 
dietary  and  as  to  the  wise  selection  among  foods  of  the  same 
type.  It  supplies  the  economic  justification  for  the  purchase 
of  certain  foods  which  would  appear  expensive  if  considered 
simply  as  sources  of  proteins,  fats,  and  carbohydrates,  and,  on 
the  other  hand,  it  shows  that  some  foods  which  are  economical 
sources  of  protein  and  energy  are  also  of  high  nutritive  value  in 
other  respects. 

Making  due  allowance  for  all  known  factors  which  affect  the 
nutritive  value  of  foods,  there  remain  large  discrepancies  be- 
tween nutritive  value  and  market  cost,  and  correspondingly 
ample  opportunity  for  the  exercise  of  true  economy  in  the 
choice  of  food  materials. 

REFERENCES 

Armsby.  The  Food  Supply  of  the  Future.  Science,  Vol.  30,  page  817 
(1909).     See  also  Ibid.,  Vol.  46,  pages  160-162  (191 7). 

Atwater.  Methods  and  Results  of  Investigation  on  the  Chemistry  and 
Economy  of  Food.  Bull.  21,  Office  of  Experiment  Stations,  U.  S. 
Dept.  Agriculture  (1895). 

Atwater.  The  Demands  of  the  Body  for  Nourishment  and  Dietary  Stand- 
ards. Fifteenth  Report  of  the  Storrs  (Conn.)  Agricultural  Experi- 
ment Station,  pages  123-146  (1903). 

Atwater.  Neue  Versuche  ueber  Stoff-  und  Kraftwechsel  im  menschlichen 
Korper.     Ergehnisse  der  Physiologic,  Vol.  3, 1,  pages  497-604  (1904). 

Benedict.  The  Nutritive  Requirements  of  the  Body.  American  Journal 
of  Physiology,  Vol.  16,  page  409  (1906). 

Chittenden.     Physiological  Economy  in  Nutrition  (1905). 

Chittenden.     The  Nutrition  of  Man  (1907). 

FoLiN.  A  Theory  of  Protein  Metabolism.  A  merican  Journal  of  Physiology, 
Vol.  13,  page  117  (1905)- 

Gephart  and  Lusk.  Analysis  and  Cost  of  Ready  to  Serve  Foods  (Amer- 
ican Medical  Association,  Chicago). 

GiLLETT.  Food  Requirements  of  Children  (Association  for  Improving 
the  Condition  of  the  Poor,  New  York). 


DIETARY  STANDARDS  AND  ECONOMIC  USE  OF  FOOD       401 

HiNDHEDE.    Protein  and  Nutrition. 

Hutchison.     Food  and  Dietetics. 

Kellogg  and  Taylor.    The  Food  Problem. 

Langworthy.  Food  and  Diet  in  the  United  States.  Reprinted  from  the 
Yearbook  of  the  U.  S.  Department  of  Agriculture  for  1907. 

LusK.     Science  of  Nutrition,  Third  Edition,  Chapters  12  and  21. 

LusK.  Food  Economics.  Journal  of  the  Washington  Academy  of  Sciences, 
Vol.  6,  page  387  (June,  1916). 

LusK.    Food  Values.    Science,  Vol.  45,  page  345  (April  13,  1917). 

McEIay.    The  Protein  Element  in  Nutrition. 

Meltzer.  Factors  of  Safety  in  Animal  Structure  and  Animal  Economy. 
Harvey  Society  Lectures,  1906-1907,  and  Science,  Vol.  25,  page  481 
(1907). 

Mendel.  Changes  in  the  Food  Supply  and  their  Relation  to  Nutrition 
(Yale  University  Press). 

Sherman  and  Gillett.  A  Study  of  the  Adequacy  and  Economy  of  Some 
City  Dietaries  (New  York  Association  for  Improving  the  Condition 
of  the  Poor). 

Taylor.  The  Diet  of  Prisoners  of  War  in  Germany.  Journal  of  the  Amer- 
ican Medical  Association,  Vol.  69,  page  1575  (191 7). 

U.  S.  Bureau  of  Labor  Statistics  (Bulletins  and  Reports). 

U.  S.  Census  Bureau  Reports. 

U.  S.  Department  of  Agriculture.  Bureau  of  Markets  (Bulletins,  Cir- 
culars and  Reports). 

U.  S.  Department  of  Agriculture,  Office  of  Experunent  Stations,  Bulls.  Nos. 
21,  29,  31,  38,  46,  52,  53,  55,  71,  75,  84,  91,  98,  107,  116,  129,  132,  149, 
150,  221,  223  (data  and  discussion  of  dietary  studies). 

U.  S.  Department  of  Agriculture,  Office  of  the  Secretary.  Reports  109, 
no.  III,  112,  113.     Meat  Situation  in  the  United  States  (1916). 

"  The  World's  Food  "  (Papers  by  several  authors)*  Annals  of  the  American 
Academy  of  Political  and  Social  Science,  Vol.  74,  pages  1-293  (November, 
1917). 


2D 


APPENDICES 

APPENDIX  A 

NOMENCLATURE  AND  CLASSIFICATION  OF  PROTEINS 

Joint  Recommendations  of  the  Committees  on  Protein  Nomen- 
clature of  the  American  Physiological  Society  and  Ameri- 
can Society  of  Biological  Chemists 

Since  a  chemical  basis  for  the  nomenclature  of  the  proteins 
is  at  present  not  possible,  it  seemed  important  to  recommend 
few  changes  in  the  names  and  definitions  of  generally  accepted 
groups,  even  though,  in  many  cases,  these  are  not  wholly  satis- 
factory.    The  recommendations  are  as  follows: 

First.  —  The  word  *'  proteid  "  should  be  abandoned. 

Second.  —  The  word  "  protein  "  should  designate  that  group 
of  substances  which  consist,  so  far  as  at  present  is  known,  es- 
sentially of  combinations  of  a-amino  acids  and  their  derivatives, 
e.g.  a-amino  acetic  acid  or  glycocoll;  a-amino  propionic  acid 
or  alanine ;  phenyl-ot-amino  propionic  acid  or  phenylalanine ; 
guanidin-a-amino  valerianic  acid  or  arginine,  etc.,  and  are 
therefore  essentially  polypeptids. 

Third.  —  That  the  following  terms  be  used  to  designate  the 
various  groups  of  proteins : 

I.  Simple  Proteins.  —  Protein  substances  which  yield  only 
a-amino  acids  or  their  derivatives  on  hydrolysis. 

Although  no  means  are  at  present  available  whereby  the 
chemical  individua^ty  of  any  protein  can  be  established,  a 
number  of  simple  proteins  have  been  isolated  from  animal  and 
vegetable  tissues  which  have  been  so  well  charac^rized  by 

403 


404  APPENDIX  A 

constancy  of  ultimate  composition  and  uniformity  of  physical 
properties  that  they  may  be  treated  as  chemical  individuals  until 
further  knowledge  makes  it  possible  to  characterize  them  more 
definitely. 

The  various  groups  of  simple  proteins  may  be  designated  as 
follows : 

(a)  Albumins.  —  Simple  proteins  soluble  in  pure  water  and 
coagulable  by  heat. 

(b)  Globulins.  —  Simple  proteins  insoluble  in  pure  water,  but 
soluble  in  neutral  solutions  of  salts  of  strong  bases  with  strong 
acids.* 

(c)  Glutelins.  —  Simple  proteins  insoluble  in  all  neutral  sol- 
vents but  readily  soluble  in  very  dilute  acids  and  alkalies.f 

{d)  Alcohol-soluble  Proteins.  —  Simple  proteins  soluble  in 
relatively  strong  alcohol  (70-80  per  cent),  but  insoluble  in  water, 
absolute  alcohol,  and  other  neutral  solvents.! 

ie)  Albuminoids.  —  Simple  proteins  which  possess  essentially 
the  same  chemical  structure  as  the  other  proteins,  but  are  char- 
acterized by  great  insolubihty  in  all  neutral  solvents.§ 

(/)  Histones.  —  Soluble  in  water  and  insoluble  in  very  dilute 
ammonia,  and,  in  the  absence  of  ammonium  salts,  insoluble  even 
in  an  excess  of  ammonia;  yield  precipitates  with  solutions  of 
other  proteins  and  a  coagulum  on  heating  which  is  easily  solu- 
ble in  very  dilute  acids.  On  hydrolysis  they  5deld  a  large 
number  of  amino  acids,  among  which  the  basic  ones  predominate. 

(g)  Protamins.  —  Simpler  polypeptids  than  the  proteins  in- 

*  The  precipitation  limits  with  ammonium  sulphate  should  not  be  made  a  basis 
for  distinguishing  the  albumins  from  the  globulins. 

t  Such  substances  occur  in  abundance  in  the  seeds  of  cereals  and  doubtless  rep- 
resent a  well-defined  group  of  simple  proteins. 

%  The  subclasses  defined  {a,  b,  c,  d)  are  exemplified  by  proteins  obtained  from 
both  plants  and  animals.  The  use  of  appropriate  prefixes  will  suffice  to  indicate 
the  origin  of  the  compounds,  e.g.  ovoglobulin,  myoalbumin,  etc. 

§  These  form  the  principal  organic  constituents  of  the  skeletal  structure  of  ani- 
mals and  also  their  external  covering  and  its  appendages.  This  definition  does  not 
provide  for  gelatin,  which  is,  however,  an  artificial  derivative  of  collagen. 


APPENDIX  A  405 

eluded  in  the  preceding  groups.  They  are  soluble  in  water,  un- 
coagulable  by  heat,  have  the  property  of  precipitating  aqueous 
solutions  of  other  proteins,  possess  strong  basic  properties,  and 
form  stable  salts  with  strong  mineral  acids.  They  yield  com- 
paratively few  amino  acids,  among  which  the  basic  amino  acids 
greatly  predominate. 

II.  Conjugated  Proteins.  —  Substances  which  contain  the 
protein  molecule  united  to  some  other  molecule  or  molecules 
otherwise  than  as  a  salt. 

(a)  Nucleo proteins.  —  Compounds  of  one  or  more  protein 
molecules  with  nucleic  acid. 

{h)  Glycoproteins.  —  Compounds  of  the  protein  molecule 
with  a  substance  or  substances  containing  a  carbohydrate 
group  other  than  a  nucleic  acid. 

(c)  P ho spho proteins.  —  Compounds  of  the  protein  molecule 
with  some,  as  yet  undefined,  phosphorus-containing  substance 
other  than  a  nucleic  acid  or  lecithin.* 

{d)  Hemoglobins.  —  Compounds  of  the  protein  molecule 
with  hematin  or  some  similar  substance. 

{e)  Lecitho proteins.  —  Compounds  of  the  protein  molecule 
with  lecithins  (lecithans,  phosphatids). 

III.  Derived  Proteins. 

I .  Primary  Protein  Derivatives.  —  Derivatives  of  the  protein 
molecule  apparently  formed  through  hydrolytic  changes  which 
involve  only  slight  alterations  of  the  protein  molecule. 

{a)  Proteans.  —  Insoluble  products  which  apparently  result 
from  the  incipient  action  of  water,  very  dilute  acids,  or  enzymes. 

{h)  Metaproteins.  —  Products  of  the  further  action  of  acids 
and  alkalies  whereby  the  molecule  is  so  far  altered  as  to  form 
products  soluble  in  very  weak  acids  and  alkalies,  but  insoluble 
in  neutral  fluids. 

*  The  accumulated  chemical  evidence  distinctly  points  to  the  propriety  of 
classifying  the  phosphoproteins  as  conjugated  compounds,  i.e.  they  are  possibly 
esters  of  some  phosphoric  acid  or  acids  and  protein. 


4o6  APPENDIX  A 

This  group  will  thus  include  the  familiar  "  acid  proteins  " 
and  "  alkali  proteins,"  not  the  salts  of  proteins  with  acids. 

(c)  Coagulated  Proteins.  —  Insoluble  products  which  result 
from  (i)  the  action  of  heat  on  their  solutions,  or  (2)  the  action 
of  alcohols  on  the  protein. 

2.  Secondary  Protein  Derivatives*  —  Products  of  the  further 
hydrolytic  cleavage  of  the  protein  molecule. 

{a)  Proteoses.  —  Soluble  in  water,  uncoagulated  by  heat,  and 
precipitated  by  saturating  their  solutions  with  ammonium  sul- 
phate or  zinc  sulphate. f 

{h)  Peptones.  —  Soluble  in  water,  uncoagulated  by  heat,  but 
not  precipitated  by  saturating  their  solutions  with  ammonium 
sulphate.J 

{c)  Peptids.  —  Definitely  characterized  combinations  of  two 
or  more  amino  acids,  the  carboxyl  group  of  one  being  united 
with  the  amino  group  of  the  other,  with  the  elimination  of  a 
molecule  of  water.§ 

*  The  term  "  secondary  hydrolytic  derivatives  "  is  used  because  the  formation  of 
the  primary  derivatives  usually  precedes  the  formation  of  these  secondary  deriva- 
tives. 

t  As  thus  defined,  this  term  does  not  strictly  cover  all  the  protein  derivatives 
commonly  called  proteoses,  e.g.  heterproteose  and  dysproteose. 

X  In  this  group  the  kyrins  may  be  included.  For  the  present  we  believe  that  it 
will  be  helpful  to  retain  this  term  as  defined,  reserving  the  expression  "peptid" 
for  the  simpler  compounds  of  definite  structure,  such  as  dipeptids,  etc. 

§  The  peptones  are  undoubtedly  peptids  or  mixtures  of  peptids,  the  latter  term 
being  at  present  used  to  designate  those  of  definite  structure. 


APPENDIX  B 
COMPOSITION   OF  FOODS 

Explanation  of  Headings 

Food  as  purchased  may  or  may  not  consist  entirely  of  edible 
material.  When  an  article  of  food  contains  inedible  matter  or 
refuse,  this  may  be  stated  separately  and  the  composition  of 
the  edible  portion  then  given,  or  the  percentages  of  refuse  and 
of  edible  nutrients  in  the  original  matter  may  be  given  so  as  to 
show  directly  the  percentage  of  each  edible  nutrient  obtained 
in  the  material  as  purchased.  For  example;  loo  pounds  of 
beef  contains  i6  pounds  of  bone  and  84  pounds  of  moist  flesh, 
of  which  15.4  pounds  are  protein,  15  pounds  fat,  53  pounds  water, 
and  0.6  pound  ash.  The  composition  may  be  stated  in  either 
of  the  following  forms: 


Composition  of  Beef 


Refuse 
Per  Cent 

Water 
Per  Cent 

Protein 
Per  Cent 

Fat 
Per  Cent 

Ash 
Per  Cent 

16.0 

53-0 

'  15-4 

15-0 

0.6 

Composition  of  Beef 

Refuse, 

Edible  Portion 

Per  Cent 

Water 
Per  Cent 

• 

Protein 
Per  Cent 

Fat 
Per  Cent 

Ash 
Per  Cent 

16.0 

63.1 

18.3 

17.9 

0.7 

407 


4o8 


APPENDIX  B 


For  most  purposes  it  is  convenient  to  include  in  one  table 
the  nutrients  calculated  both  on  the  basis  of  edible  material 
and  of  material  as  purchased.  In  such  a  case  the  percentage  of 
refuse  in  the  material  as  purchased  may  be  given  or  may  be 
omitted  as  in  the  following  form : 

Composition  of  Beef 


Water 

Protein 

Fat 

Ash 

Edible   portion    (E.    P.) 
As  purchased  (A.  P.)      . 

63.1 
53-0 

18.3 
154 

17.9 
15.0 

0.7 
0.6 

In  order  to  avoid  confusion  and  possible  errors  in  taking 
data  from  tables  of  composition  it  is  important  to  note  in 
which  form  the  percentages  are  stated.  Data  given  in  either 
form  are  of  course  readily  convertible  into  the  other.  In  Table 
I  which  follows,  the  percentages  of  nutrients  and  the  correspond- 
ing energy  values  are  stated  in  the  form  last  illustrated  above. 
Table  II  shows  percentages  of  ash  constituents  in  the  edible 
portion  only.  Table  III  shows  grams  of  protein  and  of  cal- 
cium, phosphorus,  and  iron  in  loo-Calorie  portions,  which  esti- 
mates may  obviously  be  used  equally  well  whether  the  food  be 
originally  recorded  in  terms  of  edible  material  or  of  material  as 
purchased. 

A  word  of  explanation  regarding  the  sources  and  reliabihty 
of  the  data  may  also  be  offered.  The  percentages  of  proteins, 
fats,  and  carbohydrates  given  in  Table  I  are  in  the  great  ma- 
jority of  cases  taken  from  the  tables  of  composition  of  American 
food  materials  compiled  by  Atwater  and  Bryant  and  published 
in  Bulletin  28  of  the  Office  of  Experiment  Stations,  U.  S.  De- 
partment of  Agriculture.  By  reference  to  this  bulletin  the  reader 
may  find  the  number  of  analyses  on  which  the  average  is  based 
and  the  maximum  and  minimum  of  the  recorded  percentages 
of  each  constituent,  as  well  as  the  percentages  of  moisture, 


APPENDIX  B  409 

ash,  and  in  some  cases  crude  fiber.  The  energy  values  given  in 
Table  I  are  computed  from  the  average  percentage  of  protein, 
fat,  and  carbohydrate  by  the  use  of  the  latest  and  most  accurate 
factors  (see  page  143).  The  data  for  ash  constituents  given  in 
Tables  II  and  III  are  based  on  a  critical  compilation  of  all  avail- 
able ash  analyses,  both  American  and  European.  In  some  cases 
only  a  single  ash  analysis  could  be  found;  in  other  cases  the 
data  given  are  averages  of  many  fairly  concordant  analyses. 
Between  these  extremes  are  data  of  all  degrees  of  probable  re- 
liability. It  does  not  seem  feasible  to  indicate  the  relative 
accuracy  of  the  estimates  for  different  articles  of  food.  In 
general  it  may  be  said  that  only  in  the  cases  of  the  more  impor- 
tant foods  are  the  ash  analyses  as  yet  sufiiciently  numerous 
and  concordant  to  justify  one  in  laying  great  emphasis  upon 
comparisons  of  one  article  of  food  with  another.  More  empha- 
sis can  properly  be  laid  upon  estimates  of  the  ash  constituents 
of  rations  or  dietaries  made  up  of  several  food  materials,  since 
in  such  cases  accidental  errors  will  tend  to  offset  each  other. 
It  is  chiefly  to  facilitate  such  calculations  that  the  tables  have 
been  made  as  complete  as  seemed  practicable  even  though  this 
necessitated  including  estimates  of  differing  reliability  on  ap- 
parently equal  terms. 

Data  which  are  based  in  part  at  least  upon  assumptions  are 
inclosed  in  parenthesis.  They  are  not  necessarily  less  accurate 
as  estimates  of  average  composition  than  are  some  of  the  di- 
rectly determined  data  of  individual  analyses. 

Since  many  unpublished  ash  analyses  have  been  included  in 
the  present  averages,  Tables  II  and  III  will  be  found  to  present 
many  differences  in  detail  from  those  published  elsewhere,  or 
in  the  first  edition  of  this  book.  The  general  trend  of  the  aver- 
ages has,  however,  not  been  materially  altered  by  the  results 
of  recent  work.      • 

Attention  may  also  be  called  to  the  fact  that  in  Table  II  the 
data  are  uniformly  given  as  percentages  of  the  elements  and 


410 


APPENDIX  B 


not  of  their  oxides.  For  the  convenience  of  those  who  may 
prefer  to  continue  to  calculate  calcium  and  phosphorus  in  terms 
of  the  oxides  as  has  been  customary  in  the  past,  Table  III  shows 
the  weights  of  CaO  and  P2O5  as  well  as  of  protein,  calcium, 
phosphorus,  and  iron  in  loo-Calorie  portions  of  foods. 

TABLE  I 
Edible  Organic  Nutrients  and  Fuel  Values  of  Foods* 


t, 


Food 


Almonds E.  P.f 

A.  P.t 
Apples E.  P. 

A.  P. 
Apricots E.  P. 

A.  P. 
Artichoke,  French  .     .     .     .  E.  P. 

A.  P. 
Asparagus,  fresh     ,     .     .     .  A.  P. 

cooked A.  P. 

Avocado E.  P. 

A.  P. 
Bacon,  smoked E.  P. 

A.  P. 
Bananas E.  P. 

A.  P. 

Barley,  pearled 

Beans,  dried 

Lima,  dried 

Lima,  fresh E.  P. 

A.  P. 


Protein 
(NX6.25) 

PER  CENT 

Fat 

PER 
CENT 

Carbo- 
hy- 
drate 

PER 
CENT 

Fuel 
Value 

PER 

Pound 
Calo- 
ries 

100 

Calorie 

Portion 

grams 

21.0 

54.9 

17.3 

2940 

15 

II-5 

30.2 

9.5 

1615 

28 

•4 

•5 

14.2 

28s 

159 

•3 

•3 

10.8 

214 

212 

I.I 

— 

134 

263 

174 

I.O 

— 

12.6 

247 

184 

3.4 

•5 

12.0 

300 

151 

1.7 

•3 

6.0 

150 

302 

1.8 

.2 

3-3 

100 

450 

2.1 

3-3 

2.2 

213 

213 

2.1 

20.1 

7-4 

993 

46 

1.4 

13.2 

4.8 

652 

70 

lo.S 

64.8 

— 

2840 

16 

9.5 

59.4 

—  - 

2372 

19 

1.3 

.6 

22.0 

447 

lOI 

.8 

•4 

14-3 

290 

156 

8.5 

I.I 

77.8 

1615 

28 

22.5 

"    1.8 

59-6 

1565 

29 

18.^ 

1.5 

65.9 

1586 

29 

7.1 

.7 

22.0 

557 

82 

3-2 

.3 

9-9 

250 

182 

*  The  percentages  of  nutrients  are  taken  from  Bull.  28,  Ofl5ce  of  Experiment 
Stations,  U.  S.  Department  of  Agriculture.  The  fuel  values  are  calculated  from 
these  percentages  by  the  use  of  the  factors  explained  in  Chapter  V,  viz.  —  protein, 
4  calories ;  fat,  9  calories ;  carbohydrate,  4  calories  per  gram. 

t  E.  P.  signifies  edible  portion ;  A.  P.  signifies  as  purchased. 


APPENDIX  B 


411 


Table  I  —  Continued 


Food 


Beans  —  Continued 

string,  fresh E.  P. 

A.  P. 
baked,  canned     .     .     .     .  A.  P. 
red  kidney,  canned  .     .     . 
Beef,  brisket,  medium  fat     .  E.  P. 

A.  P. 
chuck,  average    .     .     .     .  E.  P. 

A.  P. 
corned,  average   .    .     .    .  E.  P. 

A.  P. 
cross  ribs,  average     .     .     .  E,  P. 

A.  P. 
dried,  salted,  and  smoked,  E.  P. 

A.  P. 
flank,  lean E.  P. 

A.  P. 
fore  quarter,  lean     .     .     .  E.  P. 

A.  P. 
fore  shank,  lean  .    .     .     .  E.  P. 

A.  P. 
heart E.  P. 

A.  P. 
hind  quarter,  lean    .     .     .  E.  P. 

A.  P. 
hind  shank,  lean       .     .     .  E.  P. 

A.  P. 
hind  shank,  fat    .     .     .     .  E.  P. 

A.  P. 
liver E.  P. 

A.  P. 
loin E.  P. 

A.  P. 

neck,  lean E.  P. 

♦  A.  P. 

neck,  medium  fat     .     .     .  E.  P. 

A.  P. 


Protein 
(NX6.25) 

Fat 

PER 

Carbo- 
hy- 
drate 

Fuel 
Value 

PER 

Pound 

100 
Calorie 
Portion 

PER  CENT 

CENT 

PER 
CENT 

Calo- 
ries 

ORAliS 

2.3 

•3 

7.4 

184 

241 

2.1 

•3 

6.9 

176 

259 

6.9 

2-5 

19.6 

583 

78 

7.0 

.2 

18.5 

471 

96 

15-8 

28.S 

• 

1449 

31 

12.0 

22.3 



1 130 

40 

19.2 

15-4 



978 

46 

15.8 

12.5 



797 

58 

15.6 

26.2 



1353 

34 

14.3 

23.8 



1230 

37 

15.9 

28.2 



1440 

32 

13.8 

24.8 



1262 

36 

30.0 

6.5 

•4 

817 

56 

26.4 

6.9 

— 

760 

60 

20.8 

II-3 

— 

838 

54 

20.5 

II.O 

— 

821 

55 

18.9 

12.2 

— 

842 

54 

14.7 

9.5 

— 

655 

69 

22.0 

6.1 

— 

647 

70 

14.0 

3.9 

— 

414 

no 

16.0 

20.4 

I.O 

1 140 

40 

14.8 

24.7 

•9 

1292 

35 

20.0 

134 

— 

907 

50 

16.7 

II. 2 

— 

757 

60 

21.9 

5-4 

— 

617 

75 

9.1 

2.2 

— 

255 

179 

20.4 

18.8 

— 

1171 

40 

9.9 

9.1 

— 

552 

83 

20.4 

4.5 

1.7 

584 

78 

20.2 

3.1 

2.5 

537 

85 

19.7 

12.7 

— 

877 

52 

17.1 

II. I 

— 

764 

60 

21.4 

8.4 

— 

732 

62 

1 5- 1 

5.9 

— 

493 

93 

20.1 

16.S 

— 

1040 

44 

14.5 

II.O 

— 

740 

61 

412 


APPENDIX  B 


Table  I  —  Continued 


Food 


Beef  —  Continued 
plate,  lean E.  P. 

A.  P. 
Porterhouse  steak    .     .     .  E.  P. 

A.  P. 

rib  rolls,  lean A.  P. 

ribs,  lean E.  P. 

A.  P. 
ribs,  fat E.  P. 

A.  P. 
round,  lean E,  P. 

A.  P. 
round,  free  from  visible  fat 
rump,  lean E,  P. 

A.  P. 
rump,  fat E.  P. 

A.  P. 
sides,  lean E,  P. 

A.  P. 
sirloin  steak E.  P. 

A.  P. 

sweetbreads A.  P. 

tenderloin A.  P. 

tongue E.  P. 

A.  P. 

Beets,  cooked E.  P. 

fresh E.  P. 

A.  P. 

Blackberries A.  P, 

Blackfish E.  P. 

A.  P. 
Bluefish E.  P. 

A.  P. 

Boston  crackers 

Brazil  nuts E.  P. 

A.  P. 


Protein 
(NX6.25) 

Fat 

PER 

Carbo- 
hy- 
drate 

Fuel 
Value 

PER 

Pound 

100 
Calorie 
Portion 

per  cent 

CENT 

PER 
CENT 

Calo- 
ries 

GRAMS 

15.6 

18.8 

1051 

43 

130 

15-5 



867 

52 

21.9 

20.4 



1230 

37 

I9.I 

17.9 



1077 

42 

20.2 

IO-5 



795 

57 

19.6 

12.0 



845 

54 

15.2 

9.3 



654 

69 

15.0 

35.6 



1721 

26 

12.7 

30.6 



1480 

31 

21.3 

7.9 



709 

64 

19-5 

7-3 



649 

70 

23.2 

2.5 



512 

87 

20.9 

13-7 



940 

49 

19.1 

II.O 



796 

57 

16.8 

35-7 



1763 

26 

12.9 

27.6 



1361 

33 

19-3 

13-2 



890 

51 

15-5 

10.6 



715 

64 

18.9 

18.5 



1099 

41 

16.5 

16.1 



960 

48 

16.8 

12. 1 



799 

57 

16.2 

24.4 



1290 

35 

18.9 

9.2 



717 

63 

14.1 

6.7 



529 

86 

2-3 

.1 

7.4 

180 

252 

1.6 

.1 

9-7 

209 

217 

1-3 

.1 

7.7 

167 

271 

1-3 

I.O 

10.9 

262 

173 

18.7 

1.3 

— 

393 

116 

7.4 

•  7 

— 

163 

279 

19.4 

1.2 

— 

402 

113 

lO.O 

.6 

— 

206 

220 

II.O 

8.5 

71. 1 

1835 

25 

17.0 

66.8 

7.0 

3162 

14 

8.6 

33-7 

3.5 

1591 

28 

APPENDIX  B 


413 


Table  I  —  Continued 


Food 


Carbo- 

Fuel 
Value 

Protein 

Fat 

hy- 

(NX6.2S) 

PER 

drate 

Pound 
Calo- 

PERCENT 

CENT 

PER 

cent 

RTKS 

6.0 

6.3 

54-0 

1345 

8.9 

1.8 

52.1 

1 189 

9.0 

3.0 

54.2 

1268 

ii.S 

1.6 

61.2 

1385 

9.1 

1.6 

53-3 

1 199 

9.6 

1.4 

51. 1 

II58 

9.4 

1.2 

54.1 

1 199 

9.2 

1-3 

53.1 

1182^ 

9.7— 

- — ^ 

-49-7 

III3 

6.4 

1.2 

77.9 

1580 

I.O 

85.0 

— 

3491 

3.0 

•5 

4.8 

162 

27.9 

61.2 

3-5 

3065 

3.8 

8.3 

•5 

417 

1.6 

•3 

5-6 

143 

1.4 

.2 

4.8 

121 

4.3 

— 

17.4 

394 

I.I 

•4 

9-3 

204 

.9 

.2 

7.4 

158 

1.8 

.5 

4-7 

139 

I.I 

.1 

2>-3 

84 

•9 

.1 

2.6 

68 

2.1 

2.8 

5-0 

243 

9.6 

I.I 

78.3 

1640 

3-2 

.6 

5.0 

173 

28.8 

35-9 

•3 

1990 

29.6 

38.3 

— 

2102 

27.7 

36.8 

4.1 

2080 

20.9 

1.0 

4-3 

499 

25-9 

33-7 

2.4 

1890 

15.9 

21.0 

.  1.4 

1170 

18.7 

27.4 

1-5 

1484 

29.9 

38.9 

2.6 

2180 

22.6 

29.5 

1.8 

164s 

27.6 

34-9 

1-3 

1945 

1.0 

.8 

16.7 

354 

•9 

.8 

15-9 

337 

Bread,  Boston  brown  .     .     . 

graham . 

rolls,  water 

toasted 

white,  homemade     .     .     . 

milk 

Vienna 

average  white      

whole  wheat 

Buckwheat  flour      .... 

Butter 

Buttermilk 

Butternuts E.  P. 

A.  P. 

Cabbage E.  P. 

A.  P. 

Calf's-foot  jelly 

Carrots,  fresh E.  P. 

A.  P. 

Cauliflower A.  P. 

Celery E.  P. 

A.  P. 
Celery  soup,  canned     .     .     . 

Cerealine 

Chard        E.  P. 

Cheese,  American  pale     .     . 

American  red       .... 

Cheddar 

cottage       

full  cream 

Fromage  de  Brie      ... 

Neufchatel 

pineapple 

roquefort 

Swiss      ........ 

Cherries,  fresh E.  P. 

A.  P. 


414 


APPENDIX  B 


Table  I  —  Continued 


Food 


Protein 

(NX6.25) 

PER  CENT 


Fat 

PER 

CENT 


Carbo- 
hy- 
drate 

PER 
CENT 


Fuel 
Value 

PER 

Pound 
Calo- 
ries 


Cherries  —  Continued 

canned A.  P, 

Chestnuts,  fresh      .     .     .     .  E.  P. 

A.  P. 

Chicken,  broilers     .     .     .     .  E.  P. 

A.  P. 

Chocolate       

Cocoa 

Cod,  dressed A.  P. 

salt E.  P. 

A.  P. 
Consomm^,  canned  .  .  .  A.  P. 
Corn,  green,  canned     .     .     . 

sweet,  fresh E.  P. 

A.  P. 

Corn  meal 

Cowpeas,  dried 

green E.  P. 

Crackers,  butter      .     .     .     .  A.  P. 

cream A.  P. 

graham A,  P. 

soda A.  P. 

water A.  P. 

Cranberries A.  P. 

Cream  ........ 

Cucumbers E.  P. 

A.  P. 

Currants,  fresh 

dried  Zante 

Dandelion  greens  .... 

Dates,  dried E.  P. 

A.  P. 

Doughnuts 

Eggplant E.  P. 

uncooked E.  P. 

A.  P. 


I.I 
6.2 
5.2 
21.5 
12.8 
12.9 
21.6 
II. I 

25-4 
19.0 

2.5 
2.8 

3-1 
1.2 
9.2 
21.4 
9.4 
9.6 
9-7 

lO.O 

9.8 
10.7 

.4 
2.5 

.8 

.7 
1.5 
2.4 

2.4 
2.1 
1.9 
6.7 
1.2 

13.4 
11.9 


.1 

5-4 

4-5 

2.5 

1.4 

48.7 

28.9 

.2 

•3 

.4 

1.2 
I.I 

•4 
1.9 
1.4 

.6 

lO.I 

12. 1 

9.4 

9.1 

8.8 

.6 

18.5 

.2 

.2 

1.7 
i.o 
2.8 

2.5 
21.0 

.3 

10.5 

9-3 


21. 1 
42.1 
35.4 


30.3 

37.7 


.4 
19.0 

19.7 

7.7 

75.4 

60.8 

22.7 

71.6 

69.7 

73.8 

73.1 

71.9 

9.9 

4.5 

3.1 

2.6 

12.8 

74.2 

10.6 

78.4 
70.6 

53-1 
5-1 


407 

1098 

920 

493 

289 

2768 

2258 

209 

473 

361 

53 

455 

459 

178 

1620 

1550 

603 

1887 

1938 

1905 

1875 

1855 

212 

883 

79 

68 

259 

1455 

277 

1575 

1416 

1941 

126 

672 

594 


APPENDIX  B 


415 


Table  I  —  Continued 


Food 


Farina 

Figs,  dried 

Flounder A.  P. 

E.  P. 

Flour,  rye 

wheat,  California  fine   .     . 

wheat,  entire 

wheat,  graham  .... 
wheat,  patent  baker's  grade 
wheat,  straight  grade  .  . 
wheat,  average  high   and 

medium 

wheat,  average  low  grade 

Fowls E.  P. 

A.  P. 

Gelatin 

Grape  butter 

Grapes E.  P. 

A.  P. 

Grapefruit E.  P. 

A.  P. 

Haddock E.  P. 

A.  P. 

Halibut  steaks E.  P. 

A.  P. 

Ham,  fresh,  lean     .     .     .     .  E.  P. 

A.  P. 

fresh,  medium      .     .     .     .  E.  P. 

A.  P. 

smoked,  lean E.  P. 

A.  P. 

Herring,  whole E.  P. 

A.  P. 

smoked t    .  E.  P. 

A.  P. 
Hominy 


Protein 

Fat 

Carbo- 
hy- 

Fuel 
Value 

100 

{NX6.2S) 

PERCENT 

PER 

cent 

drate 
per 

CENT 

Pound 
Calo- 
ries 

Portion 

GRAMS 

II.O 

1.4 

76.3 

1640 

28 

4.3 

.3 

74.2 

1437 

32 

5-4 

•3 

— 

no 

412 

14.2 

.6 

— 

282 

161 

6.8 

.9 

78.7 

1590 

29 

7.9 

1.4 

76.4 

1585 

29 

13.8 

1.9 

71.9 

1630 

28 

13.3 

2.2 

71.4 

1628 

28 

13.3 

1.5 

72.7 

1623 

28 

10.8 

I.I 

74.8 

1608 

28 

11.4 

1.0 

7S.I 

1610 

28 

14.0 

1.9 

71.2 

1625 

28 

19.3 

16.3 

— 

1017 

45 

13.7 

12.3 

— 

752 

60 

91.4 

.1 

— 

1660 

27 

1.2 

.1 

58.S 

1088 

42 

1-3 

1.6 

19.2 

437 

104 

I.O 

1.2 

14.4 

328 

138 

.6 

.1 

12.2 

23s 

193 

•4 

,1 

8.9 

172 

264 

17.2 

•3 

— 

324 

140 

8.4 

.2 

— 

160 

283 

18.6 

5^2 

— 

550 

83 

15.3 

44 

— 

457 

100 

25.0 

14.4 

— 

1042 

44 

24.8 

14.2 

— 

1030 

44 

15-3 

28.9 

— 

1458 

31 

13-5 

25-9 

— 

1303 

35 

19.8 

20.8 

— 

1209 

38 

17.S 

18.5 

— 

1073 

42 

I9-S 

7-1 

— 

644 

70 

II. 2 

3.9 

— 

362 

125 

36.9 

1S.8 

— 

1315 

35 

20.5 

8.8 

— 

731 

62 

8.3 

.6 

79.0 

1609 

28 

41 6 


APPENDIX  B 


Table  I  —  Continued 


Food 


Honey 

Huckleberries 

Kohl-rabi E.  P. 

Koumiss 

Lamb,  breast E.  P. 

A.  P. 
chops,  broiled      .     .     .     .  E.  P. 

fore  quarter E.  P. 

A.  P. 

hind  quarter E.  P. 

A.  P. 

leg,  roast 

side E.  P. 

A.  P. 

Lard,  refined 

Lemon  juice 

Lemons E.  P. 

A.  P. 

Lettuce E.  P. 

A.  P. 

Liver,  beef E.  P. 

A.  P. 

veal E.  P. 

Lobster,  whole E.  P. 

A.  P. 

canned A.  P. 

Macaroni 

Macaroons 

Mackerel E.  P. 

A.  P. 

salt E.  P. 

A.  P. 
Marmalade,  orange      .     .     . 
Milk,  condensed,  sweetened 

skimmed 

whole 


Protein 

Fat 

Carbo- 
hy- 

Fuel 

Value 

ICX5 

(NX6.2S) 

PER 

drate 

Pound 
Calo- 

PERCENT 

CENT 

PER 
CENT 

GRAMS 

ries 

•4 



81.2 

1481 

31 

.6 

.6 

16.6 

336 

13s 

2.0 

.1 

5-5 

140 

324 

2.8 

2.1 

5-4 

234 

194 

I9.I 

23.6 

— 

1311 

35 

15-4 

19.1 

— 

1058 

43 

21.7 

29.9 

— 

1614 

28 

18.3 

25.8 

— 

1385 

33 

14.9 

21.0 

— 

1127 

40 

19.6 

19.1 

— 

1149 

40 

16.S 

16.1 

— 

953 

48 

19.7 

12.7 

— 

876 

52 

17.6 

23.1 

— 

1263 

36 

14.1 

18.7 

— 

1015 

45 

— 

lOO.O 

— 

4080 

II 

— 

— 

9.8 

178 

255 

I.O 

.7 

8.5 

201 

226 

.7 

.5 

5-9 

140 

323 

1.2 

.3 

2.9 

87 

525 

1.0 

.2 

2-5 

72 

633 

20.4 

4-5 

1.7 

583 

78 

20.2 

3-1 

2.5 

538 

84 

19.0 

5-3 

— 

562 

81 

16.4 

1.8 

.4 

379 

120 

5-9 

.7 

.2 

139 

326 

18.1 

I.I 

•5 

382 

119 

13.4 

.9 

74.1 

1625 

28 

6.5 

15.2 

65.2 

1922 

24 

18.7 

7-1 

— 

629 

72 

10.2 

4.2 

— 

356 

127 

21. 1 

22.6 

— 

1305 

35 

16.3 

17.4 

— 

1005 

45 

.6 

.1 

84.5 

1548 

29 

8.8 

8.3 

54. 1 

1480 

31 

3.4 

.3 

5-1 

167 

273 

3-3 

4.0^ 

5-0 

314 

14s 

APPENDIX  B 


417 


Table  I  —  Continued 


Food 


M'.^r         '/,  commercial 

homemade 

Molasses,  cane 

Mushrooms V,  P. 

Muskmelons E,  P, 

A.  P. 

Mutton,  fore  quarter  .     .     .  E.  P. 

A.  P. 

hind  quarter E.  P, 

A.  P. 

leg E.  P. 

A.  P. 

side .  A.  P. 

E.  P. 

Nectarines E.  P. 

A.  P. 

Oatmeal 

Okra E.  P. 

A.  P. 

Olives,  green E,  P. 

A.  P. 

ripe E.  P. 

A.  P. 

Onions,  fresh E.  P. 

A.  P. 

Oranges E.  P. 

A.  P. 
Oxtail  soup,  canned     .     .     .  A.  P. 

Oysters E.  P. 

in  shell A.  P. 

canned A.  P. 

Parsnips E.  P. 

A.  P. 
Pea  soup,  canned  .  .  .  .  A.  P. 
Peaches,  canned      .  %     .     .  A,  P. 

fresh E.  P. 

A.  P. 


Protein 

Fat 

Carbo- 
hy- 

Fuel 
Value 

100 

(NX6.25) 

PER 

drate 

PER 

Calorie 

PER  CENT 

CENT 

PER 

CENT 

Calo- 
ries 

GRAMS 

6.7 

1.4 

60.2 

1280 

36 

4.8 

6.7 

32.1 

942 

48 

2.4 



69-3 

1302 

35 

3-5 

•4 

6.8 

204 

223 

.6 

— 

9.3 

180 

252 

•3 

— 

4.6 

89 

5^o 

15.6 

30.9 

— 

1543 

29 

12.3 

24-5 

— 

1223 

37 

16.7 

28.1 

— 

1450 

31 

13.8 

23.2 

— 

1197 

38 

19.8 

12.4 

— 

863 

52 

16.S 

10.3 

— 

718 

63 

13.0 

24.0 

— 

1215 

37 

16.2 

29.8 

— 

1512 

30 

.6 

— 

iS-9 

299 

152 

.6 

— 

14.8 

280 

162 

16.1 

7.2 
.2^ 

--67^^- 

t8tt 

2^ 

1.6 

7.4 

172 

264 

1.4 

.2 

6.5 

152 

300 

I.I 

27.6 

11.6 

1357 

33 

.8 

20.2 

8.5 

995 

46 

1.7 

25.0 

4.3 

1 130 

40 

1.4 

21.0- 

3-5 

947 

48 

1.6 

•3 

9.9 

220 

206 

1.4 

.3 

•8.9 

199 

228 

.8 

.2 

11.6 

233 

195 

.6 

.1 

8.5 

169 

268 

3.8 

•5 

4.2 

166 

274 

6.2 

1.2 

3-7 

228 

199 

1.2 

.2 

.7 

43 

1065 

8.8 

2.4 

3.9 

328 

138 

1.6 

•5 

13-5 

294 

154 

1.3 

.4 

10.8 

236 

192 

3.6 

.7 

7.6 

232 

196 

•7 

.1 

10.8 

213 

213 

.7 

.1 

9.4 

188 

242 

•5 

.1 

7.7 

153 

297 

4i8 


APPENDIX  B 


Table  I  —  Continued 


Food 


Peanuts E.  P, 

A.  P, 

Pears,  fresh E.  P, 

A.  P 

Peas,  canned A.  P. 

dried 

green E.  P, 

A.  P. 

Peppers,  green E.  P. 

Persimmons E.  P. 

Pies,  apple 

custard 

lemon 

mince 

squash    .     

Pineapples,  fresh     .     .     .     .  E.  P. 

canned A,  P. 

Pine  nuts  (pignolias)    .     .     . 
Pistachios,  shelled  .... 

Plums E.  P. 

A.  P. 

Pomegranates E.  P. 

Pork,  chops,  medium  .     .     .  E.  P. 

A.  P. 

chuck  ribs  and  shoulder    .  E.  P. 

A.  P. 

fat,  salt A.  P. 

sausage .  A.  P. 

side E.  P. 

A.  P. 

tenderloin A.  P. 

Potato  chips A.  P. 

Potatoes,  white,  raw    .     .     .  E.  P, 
A.  P. 

sweet,  raw E.  P, 

A.  P. 


Protein 
(NX6.25) 

PER  CENT 


25.8 

19-5 
.6 

•5 
3.6 
24.6 
7.0 
3.6 
I.I 

.8 

3.1 

4.2 

3.6 

5-8 

4.4 

•4 

•4 

33.9 

22.3 

i.o 

.9 

1.5 

16.6 

13.4 

17.3 

14.1 

1.9 

130 

9.1 

8.0 

18.9 

6.8 

2.2 

1.8 

1.8 

1.4 


Fat 

PER 
CENT 


38.6 
29.1 

•5 

•4 

.2 

1.0 

.5 
.2 
.1 

.7 
9.8 

6.3 

10. 1 

12.3 

8.4 

•3 

.7 

49.4 

54-0 


1.6 
30.1 
24.2 
31. 1 
25-5 
86.2 
44.2 

55.3 
49.0 
130 
39.8 
.1 
.1 

.7 
.6 


Carbo- 
hy- 
drate 

PER 
CENT 


24.4 

18.S 

14.1 

12.7 

9.8 

62.0 

16.9 

9.8 

4.6 

31.S 
42.8 
26.1 
37.4 
38.1 
21.7 

9-7 
36.4 

6.9 
16.3 
20.1 
19.1 
19-5 


46.7 
18.4 
14.7 
27.4 
21.9 


Fuel 
Value 

PER 

Pound 
Calo- 
ries 


2490 

1877 

288 

256 

252 

1611 

454 

252 

109 

615 

1233 

806 

1156 

1300 

817 
196 

695 
2757 
2900 

383 

363 

447 

1530 

1230 

1585 
1298 

3555 
2030 

2423 
2145 
875 
2598 
378 
302 
558 
447 


APPENDIX  B 


419 


Table  I  —  Continued 


Food 


Prunes,  dried 
Pumpkins  .  . 
Radishes  .  . 
Raisins       .     . 


E.  P. 
A.  P. 
E.  P. 


A.  P. 
E.  P. 
A.  P. 
E.  P. 
A.  P. 


Raspberries,  red 
black      .     .  ^ 
Rhubarb    .     . 


E.  P. 
A.  P. 


Rice      .     .     . 
Salmon,  dressed 
whole     .     . 


Sausage,  Bologna 

farmer    .     .     . 

Shad,  whole   .     . 


A.  P. 
E.  P. 
A.  P. 
E.  P. 


roe     .     .     . 
Shredded  wheat 
Spinach,  fresh 
Squash  .     .     . 


A.  P. 
E.  P. 
A.  P. 
E.  P. 
A.  P. 


A.  P. 
E.  P. 
A.  P. 


Strawberries  .     .     . 
Succotash,  canned  . 

Sugar    

Tomatoes,  fresh  .     . 

canned   .... 

Tuna  (tunny  fish)    . 

Turkey      .... 

sandwich,  canned 


A.  P. 
A.  P. 


E.  P. 


E.  P. 
A.  P. 


Protein 

Fat 

Carbo- 
hy- 

Fuel 
Value 

(NX6.2S) 

PER 

drate 

Pound 
Calo- 

PER CENT 

CENT 

PER 

cent 

ries 

2.1 



73.3 

1368 

1.8 



62.2 

1 160 

I.O 

.1 

5.2 

117 

•5 

.1 

2.6 

60 

1.3 

,1 

5.8 

^33 

.9 

.1 

4.0 

91 

2.6 

3-3 

76.1 

1562 

2.3 

3-0 

68.5 

1407 

1.0 

— 

12.6 

247 

1-7 

1.0 

12.6 

300 

.6 

.7 

3.6 

los 

•4 

•4 

2.2 

63 

8.0 

•3 

79.0 

1591 

13.8 

8.1 

— 

582 

22.0 

12.8 

— 

923 

15.3 

8.9 

— 

642 

18.7 

17.6 

•3 

1061 

18.2 

19.7 

— 

1135 

29.0 

42.0 

— 

2240 

27.9 

40.4 

— 

2156 

.   18.8 

9-5 

— 

727 

9.4 

4.8 

— 

367 

20.9 

3.8 

2.6 

582 

lo.s 

1.4 

77.9 

1660 

2.1 

•3 

3-2 

109 

1.4 

•5 

9.0 

209 

•7 

.2 

4.5 

103 

1.0 

.6 

7-4 

169 

3.6 

1.0 

18.6 

444 

— 

— 

lOO.O 

•  1815 

•9 

•4 

3-9 

104 

1.2 

.2 

4.0 

103 

26.6 

11.4 

— 

946 

21. 1 

22.9 

— 

1320 

16.1 

18.4 

— 

1042 

20.7 

29.2 

— 

1568 

420 


APPENDIX  B 


Table  I  —  Continued 


Food 


1  arnips E.  P. 

A.  P. 

Veal,  breast E.  P. 

A.  P. 

cutlet E.  P. 

A.  P. 

fore  quarter E.  P. 

A.  P. 

hind  quarter E,  P. 

A.  P. 

side E.  P. 

A.  P. 
Vegetable  soup,  canned    .     . 
Walnuts,  California  or  Eng- 
lish   E.  P. 

A.  P. 

black E.  P. 

A.  P. 

Watermelons E.  P. 

A.  P. 

Wheat,  cracked 

Whitefish E.  P. 


A.  P. 


Zwieback 


Protein 

Fat 

Carbo- 

HY- 

Fuel 
Value 

(NX6.25) 

PER 

DRAPE 

PER  CENT 

CENT 

PER 

CENT 

Calo- 
ries 

1.3 

.2 

8.1 

178 

•9 

.1 

5-7 

124 

20.3 

II.O 

— 

817 

15-3 

8.6 

— 

629 

20.3 

7.7 

— 

683 

20.1 

7-5 

— 

670 

20.0 

8.0 

— 

690 

I5-I 

6.0 

— 

517 

20.7 

8-3 

— 

715 

16.2 

6.6 

-  — 

534 

20.2 

8.1 

— 

697 

15.6 

6.3 

— 

539 

2.9 

— 

•5 

62 

18.4 

64.4 

I3-0 

3199 

4.9 

17-3 

3-5 

859 

27.6 

56.3 

II. 7 

301 1 

7.2 

14.6 

30 

780 

•4 

.2 

6.7 

136 

.2 

.1 

2.7 

57 

II. I 

1-7 

75.5 

1635 

22.9 

6.5 

— 

680 

10.6 

3.0 

— 

315 

9.8 

9.9 

73-5 

1915 

256 
367 

56 

72 

66 
68 
66 
88 
64 
85 
65 
84 
735 

14 
53 
15 

59 

332 

800 

28 

67 
144 

24 


APPENDIX  B 


421 


TABLE  II 

Ash  Constituents  of  Foods  in  Percentage  of  the  Edible  Portion 
(Compiled  from  Various  Sources) 


Food 


2^ 

6 


vii4 


S3 


Siz; 


Almonds 
Apples 

dried 
Apricots 

dried 
Asparagus 
Bacon  (See  Meat) 
Bananas  .     .     . 
Bariey,  entire    . 

pearled  .  . 
Beans,  dried 

kidney,  dry    . 

Lima,  dry 

Lima,  fresh    . 

string,  fresh  . 
Beef  (See  Meat) 
Beer  .  . 
Beets  .  . 
Blackberries 
Blood  (avg.) 
Blueberries 
Bluefish  (See  Fish) 
Bread, 

Boston  brown 

"entire  wheat 

graham      .     . 

rye   ... 

white  .  .  . 
Breadfruit  .  . 
Brussels  sprouts 
Buckwheat  flour 
Butter  .  .  . 
Buttermilk    .     . 


.239 
.007 
.032 
.014 
(.066) 
.025 


.009 

•043 
.020 
.160 
.132 
.071 
.028 
.046 

.004 
.029 
.017 
.008 
.020 


.129 
(.05) 
(.05) 
.024 
.027 
.084 
.027 
.039 
.015 
.105 


•251 
.008 

.037 
.010 

(•047) 
.011 

.028 
•  iji 

(.070) 
.156 
•139 
.188 

(.070) 
.025 

.008 
.021 
.021 
.004 
.007 


.078 
(•05) 
(.05) 
•039 
.023 
.007 
.040 
.048 
.001 
,016 


.741 
.127 
(.623) 
.248 

(1.157) 
.196 

.401 
.477 
(.241) 
1.229 
1. 144 
1. 741 

(.613) 
.247 

.058 

•353 
.169 

■075 
•051 


(.232) 
(.208) 
(.291) 

•151 
.108 

•235 
.375 
.130 
.014 
.151 


.019 
.011 

(•050) 
.038 

(•177) 
.007 

.034 
.076 

(.0^7) 
.097 
.041 
.249 

(.088) 
.019 

.013 

•093 
(.007) 
.261 
.016 


(•394) 
(•394) 
(.394) 
.701 

(•394) 
.027 
.004 
.027 

(.788) 
.064 


•465 
.012 
.048 
.025 
(.117) 
.039 

.031 
.400 
.181 
.471 
.475 
•338 

.133 
.052 

.028 
•039 
.034 
.031 
.008 


185 
(.175) 
(.218) 
.148 

•093 
.068 
.120 
.226 
.017 
.097 


•037 

.005 
(.025) 

.002 
(.009) 

•039 

.125 
.016 

(.016) 
.032 
.041 
.026 

(.009) 
.024 

.006 
.058 
(.010) 
.280 
.008 


(.607) 

(.607) 

(.607) 

1.025 

(.607) 

.100 

.040 

.012 

(1.212) 

099 


.160 
.006 

? 
.010 

? 

.041 


.153 

(.120) 

•215 
.227 
.161 

(•057) 
.030 

•015 
.016 
.020 

•137 
.011 


.201 
(.120) 

150 
104 

105 
049 
194 
071 
(.010) 
026 


.0039 
.0003 
(•0015) 
(.0003) 
(.0014) 
.0010 


.0006 
.0041 
(.0020) 
.0070 
.0072 
.0070 
.0020 


.0001 
.0006 
.0006 
.0526 
.0009 


(.0030) 
(.0016) 
(.0025) 
(.0016) 
.0009 

(.0011) 
.0012 
.0002 
.00025 


422 


APPENDIX  B 
Table  II  —  Continued 


Food 


Cabbage 045 

Cabbage  greens      .     .106 
Cantaloupe   ,     .     .     .017 

Capers 122 

Carp  (See  Fish) 

Carrots 056 

Cauliflower  .     .     .     .123 

Caviar 137 

Celery 078 

Chard 150 

Cheese 931 

Cherries 019 

Cherry  juice      .     .     .01 7 
Chestnuts     .     .     .     .034 
Chicken  (See  Meat) 
Chocolate      .     .     .     .092 

Cider 008 

Citron 121 

Clams,  round     .     .     .106 
soft,  long  .     .     .     .124 

Cocoa 112 

Coconut,  dried  .     ,     .059 

fresh 024 

Coconut  milk     .     .     .020 

Cod  (See  Fish) 

Corn  (maize), mature   .020 

meal 018 

sweet 006 

sweet,  dried   .     .     .021 
Cotton-seed  meal  .     .265 

Cowpeas 100 

Crackers 022 

Cranberries  ,     .     .     .018 

Cream 086 

Cucumbers    .     .     .     .016 

Currants,  dried      .     .082 

fresh 026 


SB 


.015 
.030 
.012 
.022 

.021 
.014 
.022 
.014 
.071 

•037 
.016 
.011 
•051 

(.293) 
.011 
.018 
.098 
.079 
.420 

.059 
.020 
.009 

.121 
.084 

•033 
.121 
.462 
.208 
.011 
.007 
.010 
.009 
.044 
.017 


^ 

p 

.247 

.027 

.512 

.025 

.235 

.061 

.209 

•051 

.287 

.101 

.222 

.068 

.422 

.874 

.316 

.084 

.318 

.086 

.089 

.606 

.213 

.023 

.200 

.013 

.560 

.065 

(.563) 

.012 

.095 

.020 

.210 

.011 

.131 

•705 

.212 

.500 

.900 

•059 

.597 

.073 

.300 

.036 

.144 

— 

.339 

.036 

.213 

•039 

.113 

.040 

,414. 

.146 

1.390 

.234 

1.402 

.161 

.100 

(.594) 

.077 

.010 

.126 

.035 

.140 

.010 

.873 

.081 

.211 

.007 

.029 
.099 

•015 
.062 

.046 
.061 
.176 

.037 
.040 
.683 
.031 
.018 
•093 

•455 
.009 

.033 
.046 
.122 
.709 

.155 
.074 
.010 

.283 

.190 

.103 

.376 

1. 193 

•456 

.102 

.013 

.067 

•033 

.195 

.038 


.024 
.068 
.041 


.036 
.050 
1.819 
.156 
.039 
.880 
.014 
.003 
.006 

(.051) 
.006 
.003 

1.220 
.910 
.051 

.239 
.120 


.045 
.146 
.014 
.050 

.037 
.040 
(.910) 
.009 
.080 
.030 
.060 
.006 


.066 

•173 
.014 


.022 
.086 

.022 

.I2A 
.263 
.Oil 
.006 
.068 

.085 
.006 
.020 
.224 
.213 
.203 
(•056) 
.028 
.008 

•151 
.III 
.046 
.167 

.485 
.240 
•125 
.007 
.030 
.020 
.044 
.014 


APPENDIX  B 


423 


Table  II  —  Continued 


Food 


^5 


|i 


r 


Currant  juice  .  . 
Dandelion     .     .     . 

Dates 

Duck  (See  Meat) 
Eggplant  .... 

Eggs 

Egg  white  .  .  . 
Egg  yolk  .... 
Endive  .  .  .  . 
Farina  .  .  .  . 
Figs,  dried    .     .     . 

fresh     .     .     .     . 
Fish* 

Flaxseed  .  .  .  . 
Flour,  buckwheat  . 

"entire  wheat"  . 

graham      .     .     . 

white    .     .     .     . 


rye 

Fowl  (See  Meat) 
Gluten  feed  .  .  . 
Goose  (See  Meat) 
Gooseberries  .  . 
Grapefruit  .  .  . 
Grape  juice  .  .  . 
Grapes  .  .  .  . 
Guava  .  .  .  . 
Haddock  (See  Fishj 
Halibut  (See  Fish) 
Ham  (See  Meat) 
Hazelnuts  .  .  . 
Herring  (See  Fish) 
Hominy    .     .     .     . 


.021 

.105 
.065 

.011 
.067 
•oiS 
.137 
.104 
.021 
.162 
.053 

.204 
.010 
.031 
•039 
.020 
.018 

.247 

.035 
.021 
.011 
.oig 
.014 


.287 
.011 


,010 
.036 
.069 

.015 
.011 
.010 
.016 
.013 
.025 
.071 
.022 

.252 
.048 
(.090) 

(.133) 
.018 
.081 


.014 
.009 
.009 
.010 
.008 


.140 
.058 


.185 
.461 
.611 


(.140) 
.140 
.160 

.115 
.380 
.120 
.964 
•303 


.901 
.130 
(.274) 
(.457) 
.115 
.463 

.250 

.197 
.161 
.106 
.197 
.384 


.618 
.174 


(.006) 
.168 
•055 

(.010) 
.143 
.156 
.075 
.109 
.065 
.046 
.012 

.050 
.027 
(.037) 
(•037) 
.060 
.019 

.420 

.038 
.004 
.005 
•015 


.019 
.020 


.018 
.072 
.056 


•034 
.180 
.014 

.524 
.038 
.125 
.116 
.036 

.627 
.176 
.238 
•364 
.092 
.289 

•542 

.031 
.020 
.011 
.031 
.030 


•354 
.144 


.004 
.099 
.228 

.024 
.106 
•155 
.094 
.167 
.076 

.043 
.014 

.022 
.012 
(.070) 
(.070) 
.074 
.055 

.090 


.005 
.002 
.005 
•045 


.067 
.046 


.005 
.017 
,070 

.016 

•195 
.216 
.166 
035 
•155 
.056 
.010 

.170 
.071 
(•180) 
.183 
.177 
.123 

.558 

.011 
.010 
.009 
.024 


.198 
(.136) 


.0041 
(.0009) 


*  Average  fish  is  estimated  to  contain  per  100  grams  of  protein  as  follows : 
o.ioQ  gram  Ca;  0.133  gram  Mg;  1.671  grams  K;  0.373  gram  Na;  1.148  grams 
P;  0.528  gram  CI;  i.iig  grams  S;  0.0055  gram  Fe. 


424 


APPENDIX  B 


Table  II  —  Continued 


Food 

h 

6 

to 

3  ta 

1^ 

8 

g5? 

B 

Honey      .... 

.004. 

.018 

.386 

.468 

,001 

.019 
.076 

.020 

.001 

.0007 

Horseradish  .     .     . 

.096 

•039 

.062 

•^  y 
.016 

.190 

Huckleberries    .     . 

.020 

.007 

.051 

.016 

.008 

.008 

.Oil 

.0009 

Huckleberry    wine 

.009 

.004 

.042 

.006 

.004 

.001 

.006 

— 

Jam* 

Jelly 

.014. 

(.010) 
.030 

(.100) 

.370 

(•013) 
.050 

.008 

(.004) 
•053 

(.007) 
•057 

(.0003) 
.0006 

Kohl-rabi      .     .     . 

.077 

.071 

Lamb   (See   Meat) 

Leeks 

c^S 

.014 
.007 
.010 

.199 
•175 
.127 

.081 

.006 

.024 
.002 

.072 
.oil 



Lemons    .... 

.0^6 

.004 
.009 

.022 

.0006 

Lemon  juice .     .     . 

.024 

.010 

.003 

.006 

Lemon,  sweet    .     . 

.030 

.006 

.442 

— 

.042 

.013 

.oi6 

— 

Lentils,  dry  .     .     . 

.107 

.101 

.877 

.062 

.438 

.050 

.277 

.0086 

Lettuce     .... 

.04.^ 

.017 
.014 

•339 
.350 

.027 
.062 

.042 
.036 

.074 
.039 

.014 
.010 

.0007 

Limes 

Lime  juice     .     .     . 

•    00 

.003 

— 

Linseed  meal     .     . 

•413 

•432 

1.083 

.251 

.741 

.085 

.396 

— 

Lupins,  dry  .     .     , 

.191 

.191 

.840 

•073 

•  520 

•034 

— 

— 

Macaroni      .     .     . 

.022 

•037 

.130 

.008 

.144 

•073 

.172 

.0012 

Mackerel  (See  F'ish) 

Mamey     .... 

.000 

.012 

•345 
•235 
•334 



.028 

.140 
.019 
.082 





Mango      .... 

.021 

.007 
.030 



.017 

.013 

■ 

Mangolds      .     .     . 

.026 

.071 

'.038 

.026 

— 

Maple  syrup      .     . 

Meatt 

Meat  extract,  solid 

.107 

•034 

.208 

.010 

.013 

(.010) 

(.005) 

(•003) 

.085 

.363 

7-347 

2.394 

2.800 

3^ii7 

— 

— 

Meat  peptone    .     . 

.025 

.124 

2.440 

.641 

1. 130 

.561 

.222 

— 

Milk  (cow's),  whole 

.120 

.012 

.143 

.051 

•093 

.106 

.034 

.00024 

(cow's),  skimmed 

(.122) 

(.012) 

(•149) 

(.052) 

(.096) 

(.110) 

(.035) 

.00025 

(cow's),         con- 

densed  .     .     . 

(.300) 

(.032) 

(•374) 

(.134) 

•235 

(.280) 

(.090) 

.0006 

*  The  percentages  of  the  ash  constituents  in  jams  are  believed  to  average  about 
two  thirds  those  of  the  corresponding  fruits. 

t  Average  meat  is  estimated  to  contain  per  100  grams  protein  as  follows :  0.058 
gram  Ca;  0.118  gram  Mg;  1.694  grams  K;  0.421  gram  Na;  1.078  grams  P;  0.378 
gram  CI;  1.146  grams  S;  0.0153  gram  Fe. 


APPENDIX  B 


425 


Table  II  —  Continued 


Food 


Milk  —  Cont. 

bufifalo  .... 

camel's      .     .     . 

goat's    .... 

human       .     .     . 

mare's  .... 

sheep's  .... 
Millet  .... 
Molasses  .... 
Mushrooms  .  .  . 
Muskmelon  .  .  . 
Mustard  .... 
Mutton  (See  Meat) 
Oatmeal   .... 

Okra 

Olives 

Onions  .... 
Oranges  .... 
Orange  juice  .  , 
Oysters  .... 
Paprika  .... 
Parsnips  .... 
Peaches    .... 

dried  .... 
Peanuts    .... 

Pears 

Pear  juice  .  .  . 
Peas,  dried    .     .     . 

fresh  .... 
Pecan  nuts  .  .  . 
Pepper,  green,  fresh 
Pepper,  black,  dry 
Pepper,  white,  dry 
Perch  (See  Fish) 
Persimmons  .  .  . 
Pineapple  .  .  . 
Plums 


.203 

.143 
.128 

•034 
.083. 
.207 
.014 
.211 
.017 
.017 
.492 

.069 
.071 
.122 
.034 
.04s 
•029 
.052 
.229 
^059 

;Ol6 

.034 
.071 

:oi5 
;oo9 
io84 
.028 
.089 
.006 
.440 
•425 

.022 
.018 
.020 


.016 
.021 
.013 
•005  • 
.007 
.008 
.167 
.068 
.016 
.012 
.260 

.110 
.010 
.002 
.016 
.012 
.011 

.037 
.164 

•034 
.010 
.056 
.180 
.011 
.cx)8 
.149 
.038 
.152 
.010 
.156 
•113 

.009 
.011 

.on 


.099 
.114 

.145 
.047 
.081 
.187 
.290 
1.349 
.384 
.235 
.761 

.344 

.035 

1.526 

.178 

.177 

.182 

.091 

2.075 

.518 

.214 

(.830) 

•654 

.132 

.140 

.903 

.285 

(•332) 

(.139) 

1. 140 


.292 
.321 
.203 


in 


.038 
.019 
.079 
.010 
.010 
.030 
.085 
.019 
.027 
.061 
.056 

.062 

.043 
.128 
.016 
.012 
.008 

.459 
.178 
.004 
.022 
.082 
.050 
.016 

.104 
.013 


•131 


.Oil 

.016 
.019 


.125 
.098 
.103 
.01 4' 

•054 
.123 
.327 
.044 
.108 
.015 

•755 

•392 
.019 
.014 

.045 
.021 
.016 
•155 
.341 
.076 
.024 
.146 

•399 
.026 
.011 
.400 
.127 

•335 
.026 
.188 
.233 

.021 
.028 
.032 


.062 
,105 
.014 

•035 
.029 
.071 
.019 

•317 
.021 
.041 
.016 

.069 

.004 
.021 
.006 
.003 
.590 
.155 
.030 
.004 

.056 
.Oil 

•035 

.024 
.050 
.013 
.312 

.029 
.002 

.051 

.002 


•037 


.129 

.051 
.014 
1.230 

.202 

.027 
.070 
.Oil 

.009 

.187 

.036 
.009 

.212 
.224 
.010 
.009 
.219 
.063 

•113 
.014 


.005 
.009 
.OOQ 


.0073 
.0003 

.0038 

.0029 
.0006 
•.0002 
.0002 
.0045 

.0006 
.0003 
(.0012) 
.0020 
.0003 

.0057 
.0017 
.0026 
.0004 


.0005 
.COO5 


426 


APPENDIX  B 


Table  II  —  Continued 


Food 

6^ 

»3 

§5. 

is 

en 

11 

Pomegranate     .     . 

.on 

.005 

.063 

.085 

.105 

.003 



.0004 

Pork    (See    Meat) 

Potatoes  .... 

.014 

.028 

.429 

.021 

.058 

.038 

.030 

.0013 

sweet    .... 

.019 

.028 

•397 

•039 

04s 

.094 

.024 

.0005 

Prunes,  dried     .     . 

•054 

•055 

1.030 

.069 

•105 

.017 

.037 

.0030 

Pumpkin  .... 

.023 

.008 

(.320) 

•065 

.059 

— 

.021 

(.0008) 

Radishes       .     .     . 

.021 

.012 

.218 

.069 

.029 

•054 

.041 

,0006 

Raisins     .... 

.064 

.083 

.820 

.133 

.132 

.082 

.051 

.0021 

Raspberries  . '  .     . 

.049 

.024 

.173 

— 

.052 

— 

.017 

,0006 

Raspberry  juice 

.021 

.016 

•134 

.005 

.012 

— 

.009 

— 

Rhubarb  .... 

.044 

.017 

.325 

.025 

.031 

.036 

.013 

.0010 

Rice,  brown  .     .     . 

— 

— 

— 

.207 

— 

— 

.0020 

white    .... 

.009 

•033 

.070 

.025 

.096 

.054 

.117 

.0009 

Romaine  (salad)     . 

•045 

.032 

.306 

.016 

.053 

.073 

.019 

— 

Rutabagas    .     .     . 

.074 

.018 

•399 

.083 

.056 

.058 

.083 

— 

Rye,  entire    .     .     . 

•05s 

.130 

.453 

.•035 

.385 

.025 

.170 

.0039 

(See  also  Bread 

and  Flour) 

Salmon  (See  Fish) 

Sapato      .... 

.026 

.008 

.179 

— 

.006 

.087 

— 

— 

Shredded  wheat     . 

.041 

.144 

— 

— 

.324 

— 

— 

.0045 

Shrimp     .... 

.096 

— 

— 

— 

— 

— 

— 

Soup,  canned     .     . 

.036 

— 

•033 

— 

.030 

— 

— 

— 

canned  vegetable 

.025 

.013 

.101 

— 

.038 

— 

.025 

— 

Spinach    .... 

.067 

.037 

•  774 

.125 

.068 

.074 

.038 

.0036 

Squash,      summer, 

seeds  removed 

.018 

.008 

.150 

.002 

— 

— 

— 

(.0006) 

with  seeds      .     . 

.024 

.012 

.180 

.004 

— 

— 

— 

(.0006) 

Squash,  winter 

.019 

.011 

•320 

.004 

— 

— 

— 

(.0006) 

Strawberries 

.041 

.019 

.147 

.050 

.028 

.006 

.014 

.0008 

Tamarind 

.007 

.021 

— 

— 

.072 

.007 

.009 

— 

Tapioca    .     . 

.023 

— 

— 

— 

.090 

.018 

.029 

.0016 

Tomatoes 

.oil 

.010 

•  275 

.010 

.026 

.034 

.014 

.oo©4 

Tomato  juice 

.006 

.010 

.310 

.015 

•oiS 

.055 

— 

— 

Truffles     .     . 

.024 

.018 

.404 

.077 

.062 

.039 

— 

— 

Turnips    .     . 

.064 

.017 

.338 

.056 

.046 

.041 

.06s 

.0005 

Turnip  tops 

•347 

.02S 

.307 

.082 

.049 

.168 

.069 

— 

APPENDIX  B 


427 


Table  II  —  Continued 


Food 

is 

if 

SB 

lg 

ei 
1^ 

|I 

Veal     (See    Meat) 

Vinegar  (cider) 

.016 

.008 

.165 

— 

.013 

— 

.017 

(.0003) 

Walnuts   .     .     . 

.080 

•134 
.034 

.287 



.358 

.005 

.040 

.061 

.172 
.167 

0021 

Water  cress  .     .     . 

.187? 

.099 

.0019 

Watermelon       .     . 

.011 

.003 

.073 

.008 

.003 

.008 

.007 

Wheat,  entire    .     . 

.045 

.133 

.473 

•039 

•423 

.068 

.181 

.0050 

(See  also  Bread 

and  Flour) 

Wheat  bran  .     .     . 

.120 

.511 

1. 217 

•154 

1. 215 

.090 

.247 

.0078 

Wheat  germ      .     . 

.071 

.342 

.296 

.722 

1.050 

.070 

.325 

— 

Wheat  gluten    .     . 

.078 

.045 

.007 

.028 

.200 

.050 

.920 

— 

Whey 

.OAA 

008 

.157 

.038 

.035 

.119 

.009 

? 

Whortleberries,  en- 

tire   .... 

.031 

.021 

.261 

.021 

.042 





flesh  only  .     .     . 

.020 

.Oil 

.087 

.018 

— 

— 

— 

Wine  (avg.)  .     .     . 

.009 

.010 

.104 

.008 

•015 

.oil 

•oiS 

(.0003) 

T 

ABLE 

III 

Protein,  Calcium,  Phosphorus,  and  Iron  in  Grams  per  100  Calories 
OF  Food  Material 

(Estimated  from  data  compiled  from  various  sources) 


Food 

Protein 

Cax- 

CIUM 

Phos- 
phorus 

Iron 
(Fe) 

CaO 

PiOs 

(Ca) 

(P) 

Grams 

Grams 

Grams 

Grams 

Grams 

Grams 

Almonds 

3.22 

.037 

.072 

.00060 

.052 

•165 

Apples •  .     . 

0.64 

.012 

.020 

.00048 

.016 

•045 

Apricots 

1.90 

.023 

.044 

.00052 

.033 

(.100) 

Asparagus 

8.10 

.122 

.177 

:o045i 

.171 

.405 

Bacon  (See  Meat) 

428 


APPENDIX  B 


Table  III  —  Continued 


Cal- 

Phos- 

Iron 
(Fe) 

Food 

Protein 

cium 
(Ca) 

phorus 

(P) 

CaO 

P2O5 

Grams 

Grams 

Grams 

Grams 

Grams 

Grams 

Bananas 

1.32 

.009 

.031 

.00061 

.012 

.072 

Beans,  dried  .     .     . 

6.52 

.047 

•137 

.00203 

.065 

.314 

kidney   .... 

5.83 

(.040) 

(.143) 

(.00216) 

(.056) 

(.326) 

Lima      .... 

5.80 

.020 

.096 

.00200 

.028 

.221 

string     .... 

5.55 

.110 

.126 

.00265 

•154 

.289 

Beef  (See  Meat) 

Beer 

■ — 

.008 

.061 

.00217 

.011 

.140 

Beets 

347 

.064 

.084 

.00130 

.089 

•193 

Blackberries  .     .     . 

2.25 

.029 

.058 

.00104 

.042 

.133 

Blueberries     .     .     . 

(0.8) 

(.027) 

(.Oil) 

(.0012) 

(.038) 

(.025) 

Bluefish  (See  Fish) 

Bread,  Boston  brown 

2.64 

.056 

.082 

(.0013) 

.079 

.187 

''entire"  wheat   . 

3-95 

(.020) 

.071 

(.00065) 

(.028) 

(.163) 

graham       .     .     . 

342 

(.020) 

.084 

(.00096) 

(.028) 

(.192) 

rye 

3-54 

.009 

.058 

.00039 

.013 

•133 

white     .... 

3.50 

.Oil 

•035 

.00035 

.015 

.081 

Brussels  sprouts 

(7-30) 

(.086) 

(.380) 

(.00349) 

(.121) 

(.870) 

Buckwheat  flour 

1.8s 

,011 

.065 

.00034 

.015 

.148 

Butter 

0.13 

.002 

.002 

.00003 

.003 

.005 

Buttermilk     ... 

8.40 

.294 

.271- 

.00070 

.411 

.621 

Cabbage    .... 

5-07 

.143 

.092 

.00349 

.200 

.210 

Cantaloupe    ,     .     . 

1.51 

.044 

.038 

.00071 

.061 

.088 

Carp  (See  Fish) 

Carrots      .... 

2.42 

.124 

.101 

.00133 

.173 

.232 

Cauliflower    .     .     . 

5.90 

403 

.200 

.00197 

.564 

459 

Celery 

1.28 

.421 

.201 

.00270 

.589 

.460 

Chard 

8.37 

.393 

.105 

(.00655) 

•550 

.240 

Cheese       .... 

6.05 

.2X2 

.156 

.00030 

.297 

•357 

Cherries     .... 

1.20? 

.025 

•039 

.00051 

.035 

.090 

Chestnuts      .     .     . 

2.55 

.014 

.044 

.00029 

.019 

.088 

Chicken  (See  Meat) 

Chocolate  .... 

2. II 

•015 

•075 

(.00044) 

.021 

.171 

Citron 

0.15 

.037 

.010 

.00099 

.052 

.023 

Clams,  long   .     .     . 

19.82 

.285 

.282 

(.00970) 

.399 

.645 

round     .... 

14.01 

.229 

.100 

(.00970) 

.321 

.228 

Cocoa   ..... 

4-35 

.023 

.143 

.00054 

.032 

.327 

Coconut     .... 

0.95 

.006 

.018 

(.00030) 

.009 

.041 

Cod  (See  Fish) 

APPENDIX  B 


429 


Table  III  —  Continued 


Cal- 

Phos- 

Iron 
(Fe) 

Food 

Protein 

cium 

phorus 

CaO 

P2O6 

(Ca) 

(P) 

Grams 

Grams 

Grams 

Grams 

Grams 

Grams 

Corn 

3.06 

.006 

.102 

.00079 

(.008) 

(.233) 

Com  meal      .... 

2-59 

.005 

•053 

.0003 

.007 

.121 

Cotton-seed  meal    .     . 

12.80 

.066 

.298 

— 

.092 

.682 

Cowpeas 

6.20 

.029 

.132 

— 

.041 

•303 

Crackers,  "soda"    .     . 

2.37 

.006 

.025 

.00036 

.008 

.057 

Cranberries    .... 

0.85 

.039 

.027 

.00129 

.054 

.062 

Cream,  18.5  per  cent  fat 

1.27 

.050 

.044 

.0001 

.072 

.100 

40  per  cent  fat     .     . 

0.58 

.020 

.020 

.00005 

.032 

•045 

Cucumbers     .... 

4.60 

.090 

.191 

.00115 

.126 

.437 

Currants,  dried  (Zante) 

0.75 

.026 

.061 

.00087 

.036 

.139 

fresh 

2.62 

.045 

.066 

.00087 

.063 

.150 

Dandelion  greens    .     . 

3.93 

.172 

.117 

.0044 

.241 

.269 

Dates 

0.60 

.019 

.016 

.00086 

.026 

.037 

Duck  (See  Meat) 

Eggplant 

4.30 

.041 

.122 

.00184 

.057 

.280 

Eggs 

9-OS 

•045 

.122 

.00205 

.063 

.279 

Egg  white      .... 

24.12 

.020 

.022 

.00020 

.028 

.050 

Egg  yolk 

4-32 

.036 

.118 

.00230 

.050 

.270 

Farina 

3-05 

.006 

.035 

.00022 

.008 

.079 

Figs 

1-35 

•051 

.037 

.00095 

.072 

.084 

Fish  (See  footnote  on  page 

423) 

Flour,  buckwheat    .... 

1.84 

.011 

.065 

.00034 

.015 

.148 

"entire"  wheat   .     . 

3.85 

.009 

.066 

.0007 

.012 

.152 

graham 

. 

3-71 

.oil 

.101 

.00100 

•015 

.232 

white  (wheat)      .     . 

3.20 

.006 

.026 

.00023 

.008 

.060 

rye 

. 

1-95 

.005 

.082 

.00037 

.007 

.188 

Fowl  (See  Meat) 

Goose  (See  Meat) 

Grapefruit 

i.iS 

.040 

.036 

.00058 

.056 

.083 

Grapes 

1.35 

.019 

.032 

.00031 

.027 

.074 

Grapejuice 

0.35 

(.011) 

.Oil 

.0003 

•015 

.025 

Haddock  (See  Fish) 

Halibut  (See  Fish) 

Ham  (See  Meat) 

Hazelnuts 



.041 

.050 

.00057 

.057 

•"5 

Herring  (See  Fish) 

Hominy 

-?  •ze 

.002 

.027 

.00025 

.002 

.063 

430 


APPENDIX  B 


Table  III  —  Continued 


Cal- 

Phos- 

Iron 
(Fe) 

Food 

Protein 

cium 
(Ca) 

phorus 
(P) 

CaO 

P2O. 

Grams 

Grams 

Grams 

Grams 

Grams 

Grams 

Honey 

0.12 

.002 

.006 

.0003 

.002 

•013 

Huckleberries 

0.82 

.027 

.oil 

.0012 

.038 

.025 

Kohl-rabi 

6.48 

•249 

.186 

.00194 

•349 

.426 

Lamb  (See  Meat) 

Lemons 

2.25 

.081 

.049 

•00135 

•113 

.112 

Lemon  juice 

— 

.060 

— 

— 

.084 

.059 

Lentils 

7.37 

.031 

.126 

.00247 

•043 

.288 

Lettuce 

6.27 

.224 

.224 

.00785 

•314 

.513 

Linseed  meal 

— 

— 

— 

Lupins 

— 

— 

— 

— 

— 

— 

Macaroni 

3-70 

.006 

.040 

.00033 

.008 

.092 

Mackerel  (See  Fish) 

Maple  syrup 

— 

•037 

(.003) 

(.001) 

•053 

(.007) 

Meat  (See  footnote  on  page 

424) 

Milk,  whole 

4-75 

.174 

.134 

.00035 

.243 

•308 

skimmed 

9-25 

(.331) 

.262 

(.00068) 

(.463) 

(.600) 

condensed,  sweetened  .     . 

2.70 

(.096) 

.072 

(.0002) 

(.135) 

.165 

condensed,  unsweetened    . 

5.75 

.189 

.146 

(.0004) 

(.264) 

.335 

Molasses 

0.83 

.074 

•01 5 

.00255 

.102 

.035 

Muskmelon 

I-5I 

•043 

.038 

.0008 

.060 

.088 

Mutton  (See  Meat) 

Oatmeal 

4.20 

.017 

.099 

.00096 

.024  . 

.226 

Olives 

0.37 

.041 

.004 

.00097 

•057 

.010 

Onions       .     .   • 

3.30 

.069 

•093 

.0010 

.097 

.212 

Oranges 

I.5S 

.088 

.040 

.00039 

.123 

.091 

Orange  juice 

1.44 

.067 

•037 

.00046 

•093 

.082 

Oysters 

12.30 

.106 

.306 

.00893 

.149 

.702 

Parsnips 

2.47 

.091 

.117 

.0009 

.128 

.268 

Peaches     

1.70 

.038 

•057 

.00073 

•053 

.130 

Peanuts 

4.70 

.013 

•073 

.00036 

.018 

.166 

Pears 

0.95 

.024 

.041 

.00047 

•033 

.093 

Peas 

6.92 

.026 

.120 

.00165 

.036 

.274 

Pecans  

1.30 

.012 

.045 

.00035 

.017 

.104 

Pepper,  green 

4.59 

•034 

•145 

.00222 

•047 

•333 

Perch  (See  Fish) 

Persimmons  ...... 

— 

— 

— 

— 

— 

— 

Pineapple,  fresh      .... 

0.92 

.041 

.064 

.00116 

.058 

.146 

APPENDIX  B 


431 


Table  III  —  Continued 


Cal- 

Phos- 

Iron 
(Fe) 

Foor 

>                         Protein 

cium 

phorus 

CaO 

TJOi 

(Ca) 

(P) 

Grams 

,  Grams 

Grams 

Grams 

Grams 

Grams 

Plums   .     .     . 

....       1.20 

.024 

.038 

.00059 

•033 

.087 

Pork  (See  Meat) 

Potatoes    .     . 

....       2.65 

.016 

.069 

.00156 

.023 

.158 

sweet     .     . 

....       1.4s 

.016 

.037 

.00041 

.023 

.084 

Prunes  .     .     . 

.     .     .     .      0.70 

.018 

•035 

.00100 

.025 

.080 

Pumpkin  .     . 

....      3.90 

.089 

.229 

(.00130) 

.125 

.525 

Radishes    .     . 

....      4.42 

•073 

.098 

.00205 

.102 

.225 

Raisins      .     . 

•     •     .     .      0.7s 

.019 

.038 

.00139 

.026 

.088 

Raspberries    . 

....       2.57 

.074 

.078 

.00091 

.104 

.178 

Rhubarb    .     . 

....       2.60 

.189 

•134 

•00433 

.264 

•307 

Rice,  brown  . 

....       2.52 

(.003) 

.060 

.00058 

(.004) 

.138 

white     .     . 

....       2.27 

.001+ 

.027 

.00026 

.003 

.063 

Rutabagas     . 

....      3.15 

.185 

.140 

— 

.259 

.322 

Rye,  entire     . 

.     .     .     .        — 

— 

— 

— 

— 

Salmon  (See  Fisl 

1) 

Shredded  wheat 

....      3.50 

.oil 

.089 

.00123 

.016 

.203 

Spinach     .     . 

....      8.79 

.281 

.285 

.01506 

•393 

•653 

Squash,  summer 

....      3-OS 

•039 

•035 

(.0013) 

•054 

.080 

winter    .     . 

....      3.10 

.040 

.061 

(.0013) 

.056 

•139 

Strawberries  . 

....      2.56 

.104 

.072 

.00205 

.146 

.164 

Tapioca     .     .     . 

.      .      .      .       O.II 

.004 

.025 

.00045 

.006 

.058 

Tomatoes       .     . 

....      3.95 

.050 

.113 

.00175 

.070 

•259 

Turnips     .     .     . 

....      3-30 

.161 

.117 

.00127 

.226 

.269 

Turnip  tops   .     . 

— 

— 

— 

— 

— 

Veal  (See  Meat) 

Vinegar,  (cider)  . 

.     .     .     .       — 

.Ill 

.090 

.00213 

.156 

.206 

Walnuts,  Califor 

nia  or  Eng- 

lish     .     .     . 

....      2.60 

.013 

•oiS 

.00030 

.018 

.116 

Water  cress    .     . 

.     .     .     .       — 

— 

— 

— 

Watermelon  .     . 

....      1.32 

.038 

.010 

(.00099) 

.053 

.023 

Wheat,  entire     . 

....      3.63? 

.013 

.118 

.00140 

.018 

.270 

Wheat  germ  .     . 

— 

— 

— 

— 

Wheat  gluten     . 

....       — 

— 

— 

— 

— 

— 

Whey    .     .     .     . 

....      3.74 

.165 

.131 

? 

.231 

.300 

Whortleberries   . 

.     .    »    ■ 

— 

— 

— 

— 

Wine  (average, 

10  per  cent 

alcohol)  .     . 

.     .     .     .       — 

.011 

.021 

.00167 

.oi6> 

.047 

INDEX 


Abdei;halden, 

amino  acids  in  blood,  120 

inorganic  iron  in  nutrition,  293-295 

physiological  chemistry,  136,  257,  308 

sulphides  in  alimentary  canal,  293 
Abel,  amino  acids  dialyzed  from  blood, 

120 
Abel,   Rowntree,   and  Turner,   removal 
of     diffusible     substances     from 
blood  of  living  animals,  136 
Absorption  in  small  intestine,  93 
Acetic  acid,  108,  109 

aldehyde,  108,  109 
Acetoacetic  acid,  116 
Acetone  bodies,  117 
Acetonitrile    poisoning,    effect    of    diet 

on  resistance  to,  350 
Acid,  acetic,  108,  109 

acetoacetic,  116,  126 

adenylic,  132 

a-ketonic,  216 

amino,  43-48,  55-68, 11 9-1 2  2,  216,  217 

aminoglutaric,  44 

aminosuccinic,  44 

aspartic,  44,  47,  60,  61,  120,  126 

/3-hydroxy,  116 

/3-ke  tonic,  116 

/3-oxybutyric,  116 

butyric,  22,  113,  116 

capric,  22 

caproic,  22,  ii6 

caprylic,  22 

carbonic,  108,  109,  275,  276 

diamino,  44,  67 

diaminomonocarboxylic,  44 

diaminotrioxydodecanic,  61 

erucic,  23 

fatty,  see  Fat 

formic,  108,  109 

glutamic  (glutaminic)!^  44,  47,  60,  61, 
120,  126 

guanylic,  132 

hypogaeic,  23 

2F  433 


Acid  —  Continued 

lactic,  75,  105,  109,  113,  124,  126,  216 

lauric,  22,  116 

linoleic,  24 

linolenic,  24 

monoaminodicarboxylic,  44 

monoaminomonocarboxylic,  43 

myristic,  22,  116 

nicotinic,  327 

nucleic,  130-137 

octoic,  113,  114 

oleic,  23 

palmitic,  22,  116 

phosphoric,  131,  132 

phycetoleic,  23 

phytic,  244 

pyruvic,  108,  109,  114,  125,  216 

stearic,  22,   116,  216 
Acid-forming  diet,  279,  282 
Acid-forming     and     base-forming     ele- 
ments in  food,  279-283 
Acidity,  76,  77,  274 
Acidosis,  117,  179,  280 
Ackroyd    and   Hopkins,    deficiencies   in 

amino  acid  supply,  136,  355 
Acrolein,  19 

Activating  substances,  76 
Activity,  muscular,  179-188,  226-229 
Adenine,  131,  132,  327 

isomer  of,  327 
Adenosine,  132 
Adenylic  acid,  132 
Agar-agar,  17 

Age,    influence    on    food    requirement, 
193-198,  229-233,  370-373 

on  protein  metaboUsm,   229-233 
Alanine,  43,  45,  47,  48,  60,  61,  120,  124, 
125,  126,  216,  403 

deamination  of,  126,  216,  403 
Albumins,  52,  54,  56,  60,  142,  404 


acid-,  54 
alkali-,  54 
coagulated. 


54,  73,  406 


434 


INDEX 


Albuminates,  54 

Albuminoids,  404 

Albumoses,  see  Proteases 

Alcohol-soluble  proteins,  52,  56,  404 

Aldoses,  3,  4,  5 

Aldrich,  chemical  nature  of  pepsin,  72 

Alexis  St.   Martin,   observations  upon, 

70 
Alimentary  glycosuria,  6 
Alkali  (Alkaline)  reserve,  280,  313 
Alkalinity,  76,  77,  274 
AUantoin,  323 

Allen,  metabolism  in  diabetes,  136 
Allose,  5 
Ahnonds,  146,  256,  269,  302,  395,  410, 

421,  427 
a-ketonic  acid,  216 

aldehyde,  120 
Altrose,  5 
Amandin,  52,  60 

Amino    acids,    43-48,    55-68,    1 19-122, 
126,  216,  217 
absorption  of,  120 
dialyzed  from  blood,  120 
disappearance  of,  121 
formation  of,  125 

saturation  capacity  of  tissues  for,  121 
separation  of,  120 
yields  of 

from  flesh,  61 
from  proteins,  60-61 
Aminooxy  purine,  132 
Aminopurine,  132 
Aminoglutaric  acid,  44 
Aminolipins,  36 
Aminosuccinic  acid,  44 
Ammonia,  relation  to  nitrogen  metabo- 
lism, 130,  136,  216,  284 
to  regulation  of  neutrality,   126,  278, 
279,  281,  283 
Ammonium  carbamate,  129 

carbonate,  129 
Amylases,  73,  74,  76,  103 
Amylolytic  enzymes,  see  Amylases 
Amylopectin,  13 
Amylopsin,  76 

in  pancreatic  juice,  73,  90 
occurrence  and  action  of,  79 
Amy  lose,  13 

o-amylose,  13 
Anaerobes,  97 


Anderson,  organic  phosphoric  acid  com- 
pound of  wheat  bran,  257 
Anderson   and   Lusk,    relation   between 
diet  and  energy  production  dur- 
ing work,  200 
Antineuritic  action,  relation  of  chemical 
structure  to,  326 
substances,  attempts  to  isolate,  323, 
324 
Antiperistalsis,  94 

Antiscorbutic    prop)erty,    of    food,    310, 
311-318 
efifect  of  cooking  upon,  314,  315 
Appetite,  80,  81 

as  dietary  standard,  361 
Apples,    146,   256,   269,   302,   395,   410, 

421,  427 
Apricots,  410,  421,  427 
Arabans,  5 
Arabinose,  4 
Araboketose,  4 
Arachin,  52 
Arginine,  44,  47,  60,  61,   72,   120,   126, 

129,  403  ^ 

Armsby,  animal  nutrition,  168,  200 
experiments  in  heat  production,   162, 

164 
food  as  body  fuel,  168 
food  supply  of  the  future,  400 
Armsby  and  Fries,  influence  of  standing 

or  lying  on  metabolism,  200 
Aron,  calcium  requirement  of  children, 
282 
experiments  with  limited  rations,  338 
nutrition  and  growth,  355 
phosphorus  in  beriberi,  322 
Aron  and  Frese,  utilization  of  different 

forms  of  food  calciimi,  282 
Aron  and  Sebauer,  calcium  for  growing 

organism,  282 
Artichoke,  410 
Ash  constituents,  xii,   234-309,  342-345, 

382,  391-401,  469,  421-431 
Asparagus,  146,  394,  410,  421,  427 
Aspartic  acid,  44,  47,  60,  61,  120,  126 
Asymmetry  of  underfed  animals,  338 
Atwater,    bomb  calorimeter,  139,  140 
chemistry  and  economy  of  food,  168, 

400 
coefl5cients   of   digestibility   in  mixed 
diet,  loi 


INDEX 


435 


At  water  —  Continued 

dietary  standards,  i8o,  363,  365,  400 
muscular  work  and    protein   metabo- 
lism, 228 
protein     sparing     action     of     carbo- 
hydrate and  fat,  214,  215 
respiration    calorimeter     experiments, 
168,  200,  400 
Atwater  and  Benedict,  fats  and  carbo- 
hydrates as  protectors  of  protein, 
232 
mechanical    efficiency    of    man,    183, 

185 
metabolism  during  sleep  and   sitting 

at  rest,  176 
metabolism  while  fasting,  188 
respiration  calorimeter,  168 
rest  experiments,  164-166 
Atwater,    Benedict,    et    al.,    respiration 

calorimeter  experiments,  200 
Atwater-Rosa-Benedict,  respiration  calo- 
rimeter,   158-163 
Atwater  and   Snell,   bomb   calorimeter. 

139,  140,  168 
Aub  and  DuBois,  basal  metabolism  of 
old  men,  200 

Babcock,  metabolic  water,  257 
Bacillus,  aerogenes  capsulatus,  97 
bifidus,  96 
coli,  96,  97 
lactis  aerogenes,  96 
Bacon,  146,  394,  410,  421,  427 
Bacteria,  in  digestive  tract,  95,  97-98 
Bailey  and  MurUn,  energy  requirement 

of  new-bom,  200 
Bananas,  146,  256,  269,  302,  395,  410, 

421,  428 
Barley,  410,  421 
Barlow's  disease,  316 
Baumann  and  Howard,  mineral  metabo- 
lism of  scurvy,  327 
Bayliss,  general  physiology,  102,  257 

nature  of  enzyme  action,  102 
Bayliss  and  Starling,  secretin,  91 
Beans,    146,    241,    256,    269,    302,    321, 

394,  410,  421,  428  • 
Beavunont,     observations    upon    Alexis 
St.  Martin,  70,  71 
on  stomach  contraction,  83,  84 
Bed  calorimeter,  160,  162,  167 


Beef,  6t,   145,  241,  256,  269,  302,  394, 

411,  412,  421,  428 
Beer,  421,  428 

Beets,  146,  394,  412,  421,  428 
Beet  sugar,  see  Sucrose 
Benedict    (F.    G.),    metabolism    during 
fasting,   200,   232,   239,   257,   263, 
272,  273,  282 
in  relation  to  acidosis,  179 
muscular  work,  200 
pulse  rate,  175,  176 
variations  in  metabolism,  179 
nutritive  requirements  of  body,  378, 

400 
per  unit  of  area,  172 
respiration  apparatus,  151,  152,  168 
Benedict  (F,  G.)  and  Carpenter,  metabo- 
lism experiments,  176, 177, 178, 200 
respiration  calorimeter,  168 
Benedict  (F.  G.)  and  Cathcart,  metabo- 
lism during  muscular  work,   187, 
188,  200 
Benedict    (F.    G.)    and    Emmes,    basal 
metabolism  of  men  and  women, 
201 
influence    of    non-oxidizable    material 
upon  metabolism,  200 
Benedict    (F.    G.)    and    Murschhauser, 
metabolism  during  muscular  work, 
182,  183 
Benedict  (F.  G.)  and  Osterberg,  human 

fat,  30 
Benedict    (F.    G.)    and    Roth,    energy 
metabolism   of  vegetarians,    190, 
191,  201 
Benedict  (F.  G.)  and  Smith,  metabolism 

of  athletes,  201 
Benedict    (F.    G.)    and   Talbot,    energy 
metabolism  in  infants,  195 
respiratory  exchange  of  infants,  201 
Benedict  (S.  R.),  uric  acid  in  metabo- 
lism, 136 
Beriberi,  310,  318-324,  327-330 
Berthelot,  bomb  calorimeter,  139 

mixed  glycerides,  26 
Betaine,  327 
/3-amylose,  13 

/3-hydroxy  acids  in  fat  metabolism,  1 16 
/3-ketonic  acid,  116 
jS-oxidation  theory,  116,  216,  217 
/3-oxybutyric  acid,  n6 


43^ 


INDEX 


Bile,  9 1 

Blackberries,  412,  421,  428 
Blackfish,  412 

Blatherwick,  effect  of  base-forming  ele- 
ments in  food,  281,  282 
Blauberg,!  mineral    metabolism    of    in- 
fants, 282 
Blood,  ash  of,  421 

glucose  content  of,  6,  104,  118 
reaction  of,  273-284 
see  also  Amino  acids 
Bloor,  metabolism  of  fat,  34,  40 
Blueberries,  421,  428 
Bluefish,  412,  428 
Blyth  and  Robertson,   mixed  glyceride 

of  butter  fat,  26 
Body  fat,  composition  of,  30-35,  142 

influence  of  food  fat,  32-34 
Body,   human,   elementary   composition 

of,  234 
Body  temperature,   regulation  of,   191- 

193,  202 
Boldireff,  on  hunger,  82 
Bomb  calorimeter,  139,  140 
Bomer,  mixed  glycerides,  26 
Bones,    calcification    and    development 
of,  343 
source  of  calcium  for  carnivora,  262 
Boutwell,  phytic  acid  of  wheat  kernel, 

257 
Braddon,     cause     and     prevention     of 

beriberi,  319,  327 
Braddon  and  Cooper,  carbohydrate  and 

vitamine  metabolism,  325,  328 
Brazil  nuts,  412 

Bread,  146,  299,  394,  413,  421,  428 
Breadfruit,  421 

Breadstuffs,  see  Grain  products 
Breithaupt  and  Cetti,  calcium  elimina- 
tion, 263 
British  gum,  14 
Browne,  butter  fat,  32,  40 

definition  of  sugar,  2 
Brussels  sprouts,  421,  428 
Buckwheat  flour,  413,  421,  428 
Bunge,    metabolism   of   iron,    287,    288, 
292,  293,  300,  301,  30s,  306 
physiological  and  pathological  chem- 
istry, 257,  308 
sodium  chloride  elimination,  238 
ase  of  salt,  238 


Bunge    and    Abderhalden,    phosphorus 
content  of  milk,  247,  248 

Bureau  of  markets,  399 

Butter,  21,  22,  146,  386-392,  394,  413, 
421,  428 

Butter  fat,  31-32,  142,  346,  356-358 
growth  promoting  property   of,   346, 
356-358 

Buttermilk,  413,  421,  428 

Butternuts,  413 

Butyric  acid,  22,  113,  116 

Cabbage,  146,  269,  302,  395,  413,  422, 

428 
Caecum,  94 

Caffeine,  effect  on  metabolism,  ref.,  202 
Calcium,   234,    260-272,   343,   344,   383, 
391-396,  421-431 
amounts  in  dietaries,  267,  268 
amounts  in  foods,  268,  269,  421-431 
elimination,  263 
function  in  body,  260,  261 
in  milk,  268 
relation  to  metabolism  of  iron,   270, 

298-299,  382-383 
requirement,  262-268 
of  children,  265,  266 
of  women,  264,  265 
Calf's  foot  jelly,  413 
Calorie,  139,  140 
Calorimetry,  direct,  158 

indirect,  154 
Camerer,    calcium   requirement   at   dif- 
ferent ages,  266 
storage  of  food  for  growth,  194 
Camerer  and  Soldner,  ash  constituents 
of   new-born    infant   and  human 
milk,    282 
Cane  sugar,  see  Sucrose 
Cannon,  action  of  pylorus,  86 
competency  of  ileocaecal  valve,  94 
explanation  of  hunger,  81,  103 
intestinal  digestion,  90 
mechanical  factors  of  digestion,  102 
movements  of  stomach  and  intestines 

during  digestion,  84 
passage  of  food  through  small  intes- 
tine, 92,  93 
psychic  contraction,  88 
Cannon    and    Washburn,    investigation 
of  hunger,  80,  81,  82,  103 


INDEX 


437 


Canteloupe,  422,  428 
Capers,  422 
Capric  acid,  22 
Caproic  acid,  22,  116 
Caprylic  acid,  22 

Carbohydrates,  1-18,  131,  142,  143 
classification,  2,  4-5 
conversion  into  fat,  iii,  112 
fermentation  of,  97 
formation  from  fat,  117,  118 
formation  from  protein,  123,  124 
metabolism     of,     104-115,     123-125, 

136-137 
oxidation  of,  105 
references,  17,  18 
respiratory  quotient  of,  no,  in 
storing  of,  in 
synthesis  of,  i,  2 
yield  from  protein,  124-127 
Carbon,  234 

Carbon  and  nitrogen  balance,  115,  156 
Carbonic  acid,  108,  109,  275,  276 
Carlson,  hunger  in  health  and  disease, 
84,  103 
hydrochloric  acid  in  gastric  juice,  87 
Carpenter,   metabolism  increase  during 
typewriting,  201 
respiratory  exchange,  169 
Carpenter   and   Murlin,    metabolism   of 

mother  and  child,  201 
Carrots,   146,   256,   269,   302,   395,   413, 

422,  428 
Casein,  47,  48,  49,  53,  58,  61,    64,    73, 
142,  225,  226,  240,  243,  246,  339, 
340,  354 
Caseinogen,  53 ;   see  also  Casein 
Catalysts,  organic,  75 
Catalyzers,  78,  79 
Cathcart,  protein  metabolism,  232 
Cauliflower,  413,  422,  428 
Caviar,  422 

Celery,  146,  395,  413,  422,  428 
Cellulose,  5,  15 
Cerealine,  413 
Cereals,  see  Grain  products 
Cetti    and    Breithaupt,    metabolism    of 

iron  while  fasting,  298 
Chamberlain,  beriberi,  320,  321,  323,  328 
Chamberlain    and    Vedder,    etiology    of 
beriberi,  328  « 

rice  E)olishings  in  beriberi,  322 


Chard,  413,  422,  428 

Cheese,    256,    269,    302,    386-392,    394, 

413,  422,  428 
Chemical  composition     of    foods,     407- 

431 
Cherries,  413,  422,  428 
Chestnuts,  146,  414,  422,  428 
Chick   and   Hume,    distribution   among 
foodstuffs  of  substances  required 
for    prevention    of    beriberi    and 
scurvy,  328 
Chicken,  61,  414,  422,  428 
Children,    food    requirements    of,    193- 
198,   200-202,   229-233,   265-268, 
300,   331-347,   355-359,   370-373, 
381-383,  400 
table  of  weights  and  rates  of  growth, 
372,  373 
Chinese  moss,  17 

Chittenden,      dietary      standard,      366, 
376,  379 
economy  in  nutrition,  232,  400 
low  protein  metabolism,  376 
nutrition  of  man,  232,  400 
protein    requirement,     218-220,    376, 
379 
Chittenden    and    Underbill,    production 
of  condition  resembling  pellagra, 
355 
Chloride  metabolism,  236,  237,  271,  272 
Chlorine,  234,  236,  237,  271,  272 
Chlorosis,  289,  290 
Chocolate,  414,  422,  428 
Cholesterol,  37,  91 
Choline,  323 
Chyme,  89 
Chymification,  71 
Cider,  422 

Circulation,  work  of,  168 
Citron,  422,  428 
Clams,  422,  428 
Cocoa,  395,  414,  422,  428 
Coconut,  422,  428 
Cod,  146,  414,  422,  428 
Coefficient  of  digestibility  of  food,   99, 

loi,  102 
Cold  storage,  399 
Collagen,  52 

Colloidal  platinum  as  catalyzer,  78 
Colloids,  12,  SI 
Colon,  94 


438 


INDEX 


Combustion,  heat  of,  139-142 
Combustion  in  body,  109 
Common  salt,  use  of,  236-238 
Comparison  of  cost  and  food  value,  391- 

400 
Composite   valuation,    391-396 
Composition   of   body,    156,    174,    175, 

234.  300,  301,  336-339 
Conarachin,  52 
Conjugated  proteins,  53 
Consomme,  414 

Corn,  146,  302,  395,  414,  422,  429 
Cornflakes,  394 

Corn  meal,  146,  394,  414,  422,  429 
Cottonseed  meal,  3^3,  354,  422,  429 
CowpeaS;  414,  422,  429 
Crackers,  394,  412,  414,  422,  429 
Cranberries,  414,  422,  429 
Cream,  394,  414,  422,  429 
Creatine,  134,  135 
Creatinine,  134,  135,  142 
Cremer,  production  of  fat  from  protein, 

127,  128 
Cresol,  98 

Cucumbers,  395,  414,  422,  429 
Currants,  146,  414,  422,  429 
Cystine,  35,  37,  43,  60,  61,  64,  126,  340 
Cytodine,  132 
Cytodine-nucleotide,  132 
Cytosine,  131,  132,  133 

Dakin,   beta  oxidation  theory,    116 
interrelations     of     protein     and     car- 
bohydrate, 124-127 
oxidations    and    reductions  in  animal 
body,  T17,  136 

Dakin   and    Dudley,    intermediary   me- 
tabolism, 136 

Dandelions,  414,  423,  429 

Daniels    and    Nichols,    nutritive    value 
of  soy  bean,  355 

DarUng,   pathological  aflSnities  of  beri- 
beri and  scurvy,  328 

Dates,  395,  414,  423,  429 

Derived  proteins,  53 

Descartes,  fermentation  in  stomach,  6q 

Dextrans,  5 

Dextrin,  5,  14,  83,  86 

Dextrose,  see  Glucose 

Dezani,  chemical  nature  of  pepsin,  72 

(/.Fructose,  see  Fructose 


(/.Glucose,  see  Glucose 

Diabetes,  116,  117,  136 

Diabetic  sugar,  see  Glucose 

Diamino  acids,  44,  67,  see  also  Arginine, 

Histidine,  Lysine 
Diaminomonocarboxylic  acids,  44 
Diaminotrioxydodecanic  acid  from  casein, 

61 
Diastase,  see  Amylase 
Dibbelt,  calcium  salts  during  pregnancy 

and  lactation,  282 
Dicalcium  phosphate,  247 
Dicysteine,  43 
Diet,  see  under  Dietaries,  Dietary,  also 

under  Food 
Dietaries,    255-257,    267-268,    271,   303, 

360-401 
Dietary  deficiencies,  3 10, 347-359, 384, 396 
Dietary  standards,  361-367,  385 
Dietary  studies,  149,  150,  364,  370,  371, 

389,  390 
DigestibiUty  of  food,  99-103 
Digestion,  gastric,  85-87 
intestinal,  89-90,  93-94 
salivary,  80,  82,  85 
Dihexoses,  5 
Dioses,  4 
Dioxy acetone,  4 
Dioxypurine,  132 
Dipeptids,  45-46    . 
Disaccharides,  4,  5,  8-1 1,  17-18,  79 
Disaccharoses,  4,  5,  8-1 1,  17-18 
Distribution   of   expenditures   for   food, 

386-390,  396-398 
"Double  bonds,"  23 
Doughnuts,  414 
Drying  oils,  24 

DuBois,  basal  metabolism  of  man,  178, 
198,  201 
metabolism  of  boys,  196,  201 
respiration  calorimetry,  201 
DuBois  and  Associates,  metabolism  in 

disease,  201 
DuBois  and   DuBois,   formula   to   esti- 
mate surface  area,  173,  201 
relation  of  body  surface  to  metabolism, 

172,  173,  174 
table  of  surface  areas,  173 
Duck,  423,  429 

Duclaux,  terminology  for  enzymes,  76 
Duodenvun,  89,  90 


INDEX 


439 


Eberle,  artificial  digestive  juice,  71 
Eckles,  effect  of  sparse  diet  upon  time 

required      to      reach      maturity, 

338 
Economic  use  of  food,  386-401 
Edestin,  49,  52,  56,  60,  142,  225,  226, 

240,  247,  339,  340 
Edie,  et  al.,  antineuritic  bases,  328 
Efficiency,  mechanical,  of  man,  181-185, 

200 
Effront,  enzymes,  103 
Egg  albumin,  49,  52,  55,  60,  240 
Egg  white,  299 
Egg  yolk,  256,  269,  302 
Eggplant,  414,  423,  429 
Eggs,  146,  241,  256,  269,  302,  386,  387, 

388,  389,  390,  391,  392,  414,  423, 

429 
Ehrlich  and  Lazarus,  medicinal    iron    in 

hemoglobin  formation,  297 
Ehrstrom,    phosphorus    metabolism    in 

man,  247,  257 
Eijkmann,  beriberi  in  fowls,  321,  322 
Elementary    composition,    30,    32,    49, 

142,  156,  234,  421-431 
Embden  and  Schmitz,  amino  acid  forma- 
tion, 125,  136 
Emmett     and      Grindley,     phosphorus 

content  of  flesh,  257 
Emmett   and   McKim,    yeast   vitamine 

fraction    as    supplement    to    rice 

diet,  328 
Endive,  423 
Energy  allowances  for  adults,  366,  367, 

370 
for  children,  370-373 
expenditure,    during    muscular    labor, 

185,  186 
metaboHsm,  148-201 

experimental  methods,  148-169 
governing  conditions,  170-201 
of  growing  infant,  195,  196 
influence  of  age  and  growth,    193, 

194 
influence  of  food,  188 
effect  of  internal  secretions,  178 
influence  of  mental  work,  177,  178 
requirement,    148-201,    366-373 
influence  of  sex,  199 
methods  of  study,  I4§r-i66 
Enterokinase,  92 


Erzymes,  6,  8,  10,  11,  69-80 

activity  of,  75,  76,  77 

amylolytic,  75 

chemical  nature  of,  71 

classification  of,  74 

coagulating,  75 

colloidal  nature  of,  72 

deaminizing,  75 

digestive,  69 

extracellular,  75 

hydrolytic,  75 

intracellular,  75,  103 

introduction  of  word,  74 

isolation  of,  74 

lipolytic,  75 

properties  of,  74 

proteolytic,  75,  97 

reducing,  75 

sugar-sphtting,  75 
Epigastrium,  81 
Eppler,    investigations    of    phosphatids, 

258 
Erepsin,  80,  92 
Ergometer,  185 
Erucic  acid,  23 
Erythrose,  4 
Erythrulose,  4 
Essential  oils,  36 
Esterase,  103 

Ethereal  sulphate,  98,  241,  242 
Ethylene  Unkage,  23 
Euler,  chemistry  of  enzymes,  103 
Evvard,    Dox,    and    Guernsey,    cystine, 
in  tissue  growth,  345 

effect  of  calcium  and  protein  fed  preg- 
nant swine  on  offspring,  282,  35s 
Excelsin,  52,  60,  225 

Factors   determining   dietary   standard, 
360,  361,  38s 
for    calculating    energy    requirement, 

186 
for   calculating   fuel   values   of   food, 
143 

Falck,  influence  of  body  fat  ujx)n  pro- 
tein metabolism,  205,  206 

Falk    and    Siguira,  lipase  preparations, 
74.  103 

Falk,     lipolytically    active    substances, 
74,  103 

Farina,  394,  415,  423,  429 


440 


INDEX 


Fasting,  i88,  189,     200,     203-206,    253, 

272,  273,  298 
Fats,  19-36,  40-41 

calories  per  gram,  142,  143 

composition  of,  30-32 

fish,  24 

food,  influence  of,  on  body  fat,  32-34 

formation    from    carbohydrates,     27- 

29,  112-115 
formation  in  nature,  27-29 
general  properties,  19-21 
hardened,  23 
heart,  30-31 
hydrolysis  of,  19 
kidney,  30-31 
liver,  30-31 
metabolism  of,  115 
of  organs,  30-31 
oxidation  of,  115 
production  from  protein,  127 
respiratory  quotient  of,  no,  in 
storage  in  body,  117 
structure  of,  19,  21-27 
Fatty  acids,  21-24,  36 
in  metabolism,  116 
unsaturated,  23-24,  31 
Fatty  oils,  19,  36 
Fat  soluble  A,  xiii,  333,  346,  347,  383, 

384;  see  also  Growth 
Feces,  99,  100,  loi,  103,  253,  254,  263, 

286,  289,  299 
Fermentation,  69,  97 
Ferments,  75  ;  see  also  Enzymes 
Fibrin,  53 
Figs,  415,  423,  429 
Filberts,  395 
Fingerling,  phosphorus  metabolism,  249. 

250,  258 
Fischer,  synthetic  polypeptids,  46,  49- 

So 
Fischer     and     Abderhalden,     diamino- 
trioxy-dodecanic  acid  from  casein, 
61 
Fish,  386,  387,  389,  390,  391,  392,  423, 

429 
Fitz,  Alsberg,  and  Henderson,  excretion 
of    phosphoric    acid    in    acidosis. 
282 
Fixed  oils,  19 
Flesh,  amino  acids  of,  61 
Fletcher,  beriberi  and  rice,  320 


Flounder,  415 

Flour,  241,  256,  269,  302,  394,  415,  423, 

429 
Fluorine,  234 

Folin,  distribution  of  excreted  nitrogen, 
135 
protein  metabolism,  137,  376,  377,  400 
Folin   and   Denis,    protein   metabolism, 
137 
relation  of  amino  acids  to  metabolism, 
119 
Food,   allowances  for  healthy  children. 
371 
analyses,  408,  409,  410-431 
antineuritic  properties  of,   310,   318- 

330 
antiscorbutic      properties      of,     310- 

318,  327-329 
composition  of,  407,  408,  409,  410-431 
digestibility  of,  99-103 
economic  use  of,  386-401 
fuel  value  of,  xii,  138-147,  407-420 
functions  of,  xi,  335 
influence  of,  on  growth,  see  Growth; 
on  metabolism,  1 88-191 ;  see  also 
under  names  of  the  different  food- 
stuffs 
nutritive  ratio  of,  147,  148 
passage  through  intestine,  92-94 
passage  through  stomach,  83-89 
requirements,  170-233,  252-267,  297- 
301,  331-385.  400,  401 
Foods,  see  Food,  see  also  under  name  of 

each 
Foodstuffs,  see  under  the  name  of  each 

definition,  xii 
Forbes,  phosphorus,  242,  251,  258 
mineral    elements   in    nutrition,    258, 

283 
effect   of    rations   upon   development 
of  swine,  258,  355 
Forbes  and  Beegle,  mineral  metabolism 

of  milch  cow,  265,  283 
Forbes  and    Keith,    functions   of    phos- 
phorus, 242,  243 
organic  and  inorganic  phosphorvs,  251 
phosphorus     compounds     in     animal 
metabolism,  258 
Formaldehyde,  i,  2 
Formic  acid,  108,  109 
Fowls,  415,  423,  429 


INDEX 


441 


Fraser  and  Stanton,  study  of  beriberi 
due  to  use  of  polished  rice,  320, 
322 

Frohlich,  infantile  scurvy,  328 

Fructose,  3,  5,  7 

Fruits,  386,  387,  388,  389,  390,  391, 
392,  395 

Fruit  sugar,  see  Fructose 

Fucose,  4 

Fuel  requirements,  see  Food  require- 
ments, Dietary  standards,  Energy 
metabolism 

Fuel  value  of  food,  138-143,  144,  145, 
147,  407-421 

Fundus,  84 

Funk,  acidosis,  315,  328 
deficiency  diseases,  328 
isolation  of  antineuritic  substance,  323 

Funk  and  Schonborn,  influence  of  vita- 
mine-free  diet  upon  carbohydrate 
metabolism,  328 

Furst,  experimental  scurvy,  328 

Galactans,  5,  8,  16 

Galactose,  5,  8,  104 

Galactosides,  8,  10 

Garrod,  scurvy,  312 

Gastric  digestion,  80,  84,  85-89 

Gastric  fistula,  70 

Gastric  juice,  70,  85-88 

Gaule,  absorption  of  inorganic  iron,  290, 

308 
Gautier,  dietary  standard,  363 
Gelling,  nutritive  value  of  diamino  acids, 

67 
Gelatin,  48,   52,   55,   57,   61,    142,   225, 

341,  41S 
as  supplement  to  oat  diet,  351 
Gephart  and  DuBois,  basal  metabolism, 

201 
Gephart  and  Lusk,  analysis  and  cost  of 

ready-to-serve  foods,  4cx) 
Gies,  classifications  of  the  lipins,  36,   40 
Gillett,   food   requirements  of   children, 

400 
Givens  and  Mendel,  calcium  and  mag- 
nesium metabolism,  283 
Gliadin,  47,  48,  49,  50,  52,  56,  58,  61, 

63,  68,   142,   224,   225,   240,   339, 

342 
Globulins,  52,  54-56,  TO,  224,  404 


Glucose,  3,    5,    6-7,    75,    104-110,    117, 

118,  124-126,  142,  216 
Glucosides,  4 

Glutamic  acid,  44,  47,  60,  61,  120,  126 
Glutaminic  acid,  see  Glutamic  acid 
Glutelins,  52,  56,  61,  404 
Gluten,  56 

Glutenin,  52,  61,  225 
Gluten  feed,  423 
Glyceric   aldehyde,    105-109,    115,    117, 

125,  216 
Glycerides,   19,  20,  24-27,  332;  see  also 

Fats 
Glycerin,  see  Glycerol 
Glycerol,*^ 1 9,  107,  115,  117,  216 
Gly  cerophosphaTeT  3  2  2 
Glycerose,  4 
Glyceryl  radicle,  19 
Glycine,  42,  45,  47,  48,  60,  61,  62,  119, 

120,  126,  403 
Glycinin,  60,  225 
Glycocoll,  see  Glycine 
Glycogen,  5,  14-15,  104,  109,  in,  123, 

137,  142,  204,  205 
Glycolaldehyde,  3,  4 
GlycoHpins,  36 
Glycolose,  3,  4 
Glycoproteins,  53,  405 
Glycosuria,  6,  124 
Glycyl  glycine,  45 
Glyoxals,  124,  125 
Goetsch,  influence  of  pituitary  feeding, 

355 
Goodall  and  Joslin,   chloride  excretion, 

238 
Goose,  423,  429 
Gooseberries,  423 
Gossypol,  353 
Gottlieb,  intestinal  elimination  of  iron, 

288,  308 
Grain  products,  386,  387,  388,  389,  390, 

391,  392,  394,  397 
Grapes,  395,  415,  423,  429 
Grape  butter,  415 
Grapefruit,  395,  415,  423,  429 
Grape  sugar,  see  Glucose 
Growth,  56-68,  193-198,  224-226,  229- 

231,   247-249,   266-267,  300-301, 

310,331-359 
Griitzner,  muscular  activity  of  stomach, 

83,84 


442 


INDEX 


Guanine,  130,  131,  132 

Guanosine,  132 

Guanylic  acid,  132 

Gulose,  s 

Gumpert,    metabolism    of    phosphorus, 

etc.,  250,  258 
Gums,  5 
Guava,  423 


Haddock,  415,  423,  429 

Halibut,  61,  415,  423,  429 

Ham,  145,  415,  423,  429 

Hammarsten's  rennin,  78 

Harden    and    Zilva,    a-hydroxypyridine 

and  adenine,  328 
Hart,  nutritive  values  of  milk  and  grain 

proteins,  66,  67 
Hart,  Halpin,  and  McCollum,  behavior 

of  chickens  fed  rations  restricted 

to  cereal  grains,  355 
Hart  and    Humphrey,  protein    require- 
ments of  milch  cows,  226 
Hart  and  McCollum,  effects  of  restricted 

rations,  328,  344,  355,  356 
Hart,  McCollum  and  Fuller,  phosphorus 

in  nutrition  of  animals,  248,  258, 

344,  355 

Hart,  McCollum  and  Humphrey,  ash 
constituents  of  wheat  bran  in 
metabolism  of  herbivora,  258 

Hart  and  Steenbock,  effect  of  magne- 
sium upon  calcium  metabolism. 
270,  283 

Hartley,  fat  of  organs,  30-31,  40 

Hasselbach,  influence  of  food  upon  car- 
bon dioxide  tension  of  expired 
air,  281 

Hausermann,  inorganic  iron  in  place 
of  food  iron,  291,  292,  293 

Hawk,  water  in  nutrition,  258 

Hazelnuts,  423,  429 

Heat  of  combustion,  139-143 

Heat  production  in  body,  see  Metab- 
olism 

Hematin,  59 

Hematogen,  287 

Hemicellulose,  16 

Hemoglobin,  53,  59,  85,  285,  297,  405 

Henderson,  acid  excretion,  273-279,  283 
acidosis,  283 


Henderson  —  Continued 

carbonic    acid    and    neutrality,    275, 

276 
equilibrium  in  solutions  of  phosphates, 

283 
fitness  of  the  environment,  283 
regulation    of    neutraUty    in    animal 

body,  273-279,  283 
Henriques      and     Andersen,     nutrition 

through     intravenous     injection, 

120,  137 
Henriques    and    Hansen,    influence    of 

food    fat    and    other    conditions 

on  body  fat  of  swine,  29,  40 
Heptoses,  5 
Herbst,     calcium    and    phosphorus    in 

growth,  258,  266,  267 
Herring,  415,  423,  429 
Herter,  bacteria  of  the  digestive  tract, 

96-98    103 
calcium  metabolism,  263,  266 
Hertz,  absorption  in  large  intestine,  93 
Hess,  infantile  scurvy,  317,  318 
Hess   and    Fish,    infantile   scurvy,    317, 

329 
Heterocj'clic  amino  acids,  44 
Hexobioses,  5 
Hexosans,  5 
Hexoses,  5,  132 
Hill,  estimation  of  relative  heights  and 

weights,  367 
glycogen  formation  during  sleep,  117, 

118 
Hindhede,    dissolving    of    uric    acid    as 

affected  by  food,  281 
proteins  and  nutrition,  223,  232,  401 
Histidine,  44,  45,  47,  60,  61,  72,  120 
His  tones,  52,  404 
Hogan,  corn  as  source  of  protein  and  ash, 

356 
Hoist  and  FrohUch,  antiscorbutic  prop- 
erty of  food,  313,  329 
Hominy,  394,  415,  423,  429 
Honey,  416,  424,  430 
Hoobler,  human  milk  production,  232 
milk  as  food  protein,  226 
protein  need  of  infants,  232 
Hopkins,    accessory    factors    in    normal 

dietaries,    356 
milk  as  growth-promoting  food,  356 
Hordein,  52,  61 


INDEX 


443 


Hormone,  88,  89,  276,  345 

Hornberg,     checking     of     secretion     of 

gastric  juice,  88 
Horseradish,  424 

Howell,  arrangement  of  food  in  stomach, 
8S 

physiology,    103 

relation  of  amino  acids  to  metabolism, 

I*      119 
Huckleberries,  416,  424,  430 
Hudek  and  Stigler,  hunger,  82 
Hull  and  Keeton,  gastric  Upase,  103 
Human  body,   elementary  composition, 

234 
Hundred-Calorie  portions,  144-146,  410- 

420 
Hunger,  81-82 

Hunt,  acetonitrile  poisoning,  350 
Hutchison,  food  and  dietetics,  401 

normal  amount  of  protein  in  diet,  376 
Hydrogen,  234 
Hydrogenation  of  fats,  23 
Hydrogen   ion   concentration,    influence 

on  enzyme  activity,  76,  77 
Hydrogen    peroxide,    decomposition   of, 

78_ 
Hydrolysis,  6,  130 
Hydrolytic  cleavage,  130 
Hypogaeic  acid,  23 
Hypoxanthine,  130,  132,  133 

Ileocecal  valve,  92,  93,  94 

Ileum,  93,  94 

Indican,  98 

Indol,  98 

Infants,  see  Children 

Inorganic  elements,     234-309,    342-345, 

347-352,  355-359,  382-383,  391- 

401,  421-431 
distribution  in  body,  234,  260 
in  American  dietaries,  271 
relation  to  each  other,  269,  270 
requirements  (quantitative),  252-255, 

262-268,  297-300,  -382-383 
Inorganic  foodstuffs,   234,  309:  see  also 

Inorganic  elements 
Inositol,  244 

Intestinal  digestion,  89-94 
Intestinal  juice,  91,  92 
Inulin,  5,  17  ^ 

Inversion  of  sugar,  9 


Invertase,  77,  103 ;  see  also  Sucrase 

Invert  sugar,  9 

Iodine,  234,  345,  350 

Iodine  number  of  fats,  23 

Irish  moss,  17 

Iron,  234,  271,  383 

assim.ilation  of,  287,  288 

function  in  nutrition,  285,  286 

in  dietaries,  303,  308,   382-383,   409 

in  eggs,  304 

in  food,  285,  303,  308,  421-431 

in  food  materials,   tables,   302,   421- 

431 
in  grain  products,  305,  306 
in  meat,  303 

in  milk,  300,  301,  304,  305 
in  modified  milk,  304,  305 
metabolism,   285-301,  306-309 
nutritive  relations  of,  297,  298 
per  cent  in  body,  285 
requirement,    297-300,    382-383 
reserve  supply  at  birth,  300 
utilization    of    different    forms,    287- 

297,  306,  308-309 
value  of  inorganic,  286,  296,  297 
vegetables  and   fruits  as   sources  of, 

306,  307 
Isomaltose,  5 
Isomerization,  326 

Jackson  et  ah,  experimental  scurvy, 
31S,  316,  329 

Jam,  424 

Janney,  metabolic  relationship  of  pro- 
teins to  glucose,  137 

Jelly,  424 

Jones,  nucleic  acids,  131,  134,  137 

Jones  and  Read,  yeast  nucleic  acid,  137 

Jordan,  Hart,  and  Patten,  metabolism 
and  physiological  efifects  of  phos- 
phorus of  wheat  bran,  258 

Jordan  and  Jenter,  formation  of  milk 
fat  from  carbohydrate,  28,  40 

Kafirin,  52 

Kastle,  alkali  in  ash  of  human  and  cow's 
milk,  283 

Katzenstein,  oxygen  consumption  dur- 
ing muscular  work,  181,  182 

Kauffmann,  metaboUsm  experiment  with 
gelatin  and  amino  acids,  55 


444 


INDEX 


Kayser,   protein-sparing  by  fat  or  car- 
bohydrates, 211,  212 
Keller,  storage  of  phosphorus,  247 
Kellogg  and  Taylor,  the  food  problem, 

401 
Kendall,  bacteria  of  digestive  tract,  95 
Kephalins,  243 
Ketoses,  3,  4,  s 
Ketoxylose,  4 
Knoop,  formation  of  amino  acids  from 

ammonium  salts,  125 
Knoop  and  Embden,  /3-oxidation  theory, 

116 
Knoop  and  Kertes,  a-amino  acids  and 

a-ketonic  acids  in  the  liver,  137 
Kohlrabi,  416,  424,  430 
Koumiss,  416 

Kreis  and  Hafner,  mixed  glycerides,  26 
Krogh,  respiratory  exchange  of  animals 

and  man,   201 
Kiihne,  introduction  of  word  "enzyme," 

74 
Kulz,     carbohydrate     formation     from 

protein,  124 
Kunkel  and  Egers,  regeneration  of  blood 

with  medicinal  iron,  291 
Kyrins,  406 

Lactalbumin,  49,  52,  56,  60,  65,  66,  68, 

225,  226,  339,  340 
Lactase,  occurrence  and  action,  79 
Lactic  acid,  75,  105-109,  113,  124,  125, 

126,  216 
Lactose,  5,  10 
Lamb,  416,  424,  430 
Landergren,  nitrogen  metabolism,  215 
Langworthy,   food   and  diet   in  United 

States,  401 
results  of  dietary  studies,  364,  365,  401 
Langworthy     and     Milner,     respiration 

calorimeter,  169 
Lard,  394,  416 
Laurie  acid,  22,  116 
Lawes   and    Gilbert,    formation    of   fat 

from  carbohydrate,  28 
Leathes,  synthesis  of  butyric  acid  from 

lactic  acid,  113 
Lecithans,  243 
Lecithins,  38-39.  243,  322,  323 

in  human  and  cow's  milk,  248 
Lecithoproteins,  53,  243,  405 


Leeks,  424 

Legumelin,  52,  60 

Legumin,  49,  52,  56,  60,  142,  240 

Leipziger,  phosphoproteins,  246 

Lemons,  395,  416,  424,  430 

juice,  416,  424,  430 
Lentils,  395,  424,  430 
Lettuce,  146,  395,  416,  424,  430 
Leucine,  43,  47,  60,  61,  72,  78,  120,  126 
Leucosin,  49,  52,  60,  240 
Levene  and  Meyer,  carbohydrate  metab- 

oHsm,  137 
Levin,  intestinal  bacteria,  95,  96 
Levulans,  5,  17 
Levulose,  see  Fructose 
Liebig,  high  protein  diet,  374,  375 
Limes,  424 
Linoleic  acid,  24 
Linolenic  acid,  24 
Linsee^  meal,  424,  428 
Lipases,  73,  74,  76,  79,  103 
Lipins,  classification  of,  36 
Lipoids,  21,  34-41 
Lipolytic  enzymes,  see  Lipases 
Litten,  scurvy,  329 
Little,    beriberi    caused    by    fine    white 

flour,  329 
Liver,    416 
Lloyd's  reagent,  325 
Lobster,  416 
Lowy  and  Zuntz,  influence  of  war  diet 

on  metabolism,  201 
Lupeose,  5 
Lupins,  424,  428 

Lusk,    calcium    rich    diet    during   preg- 
nancy, 265 

chemical    regulation    of    temperature, 
192 

energy  requirements,  180,  187 

food  economics,  401 

food  values,  401 

formation  of  carbohydrate  from  pro- 
tein, 124 

hydrolysis  of  nucleotides,  132 

influence  of  food  on  metabolism,  190, 
201 

nutrition,    117,    137,    169,    201,    232, 
283,  329,  356,  401 

protein  metabolism,  211 
and  muscular  activity,  229 

regulation  of  metabolism,  178 


INDEX 


445 


Lusk  —  Continued 

specific  dynamic  action,  igo,  201 
yield   of   carbohydrate   from   protein, 

127 
Lusk,  Rich,  and  Soderstrom,  respiration 

calorimeter,  169 
Lyman,  metabolism  of  fats,  137 
Lymphatic  radicles,  90 
Lysine,  44,  47,  48,  60,  61,  62,  63,  72,  120, 

216,  224,  226,  339,  341,  342 
Lyxose,  4 

Macallum,  absorption  of  iron,  290,  309 
MacLean  and  Williams,   fat  of   tissues 
and  organs,  40 

phospholipins  in  liver  fat,  39 
McClendon,  formation  of  fat  from  pro- 
tein, 40 
McCollum,  causes  of  failure  of  food  to 
nourish,  347,  348 

deficiencies  of  individual  foods,   334, 
335,  347,  352,  356 

dietary  relationships  among  foods,  329, 
356 

effect  of  acid-forming  food,  281 

fat-soluble  A  in  plant  tissue,  333 

growth  and  development,  334,  346 

growth  promoting  property  of  butter 
fat,  346 

nuclein  synthesis,  258 

nutritive  values  of  milk  and  grain  pro- 
tein, 66,  67,  226,  232,  356 

repair  processes  in  protein  metabolism, 
232 

value  of  inorganic  phosphates,  248,  249 
McCollum  and  Davis,  essential  factors 
in  diet  during  growth,  356 

growth  promoting  influence  of  butter 
fat,  39,  332,  356 

influence  of  certain  vegetable  fats  on 
growth,  356 

influence  of  mineral  content  of  ration 
on  growth,  356 

influence  of  plane  of  protein  intake  on 
growth,  232,  356 

nature  of  dietary  deficiencies  of  rice, 
356 

nutrition    with    purified     food     sub- 
stances, 356 
McCollum,  Halpin,  a^fl  Drescher,  syn- 
thesis of  lecithin,  249,  258 


thesis 


McCollum  and  Hoagland,  endogenous 
nitrogen  metabolism,  283 

McCollum  and  Kennedy,  dietary  fac- 
tors in  production  of  polyneuritis, 
329,  347 

McCollum  and  Pitz,  vitamir 
and  deficiency  diseas 

McCollum    and    Simmonds, 
analysis      of     pella 
diets,  356 

McCollum,  Simmonds,  and  Pitz,  dietary 
deficiencies  of  the  maize  kernel, 
357 

of  oat  kernel,  357 
of  wheat  embryo,  356 
of  white  bean,  357 
distribution  in  plants  of  fat   soluble 

A,  357 
effects  of  feeding   proteins   of   wheat 
kernel  at  different  planes  of  in- 
take, 232,  357 
effect    upon    growth    of    adding    salt 

mixture  to  ration,  34s 
is  lysine  the  Umiting  amino  acid  in 
proteins  of  wheat,  maize,  or  oat 
kernel?,  357 
relation   of   unidentified   dietary   fac- 
tors  to   growth-promoting   prop- 
erties of  milk,  357 
vegetarian    diet    in    light    of    present 
knowledge  of  nutrition,  357 

McCrudden,  nutrition  and  growth  of 
bone,  357 

McCrudden  and  Fales,  mineral  metabo- 
lism in  intestinal  infantiUsm,  258 

McKay,  protein  element  in  nutrition, 
232,  401 

Maize,    350,    351 

Maize  glutelin,'6i,  225 

Macaroni,  394,  416,  424 

Mackerel,  416,  424,  428 

Magnesium,  234,  271,  272 

Magnus-Levy,  respiratory  quotient  and 
metabolism,  iii,  154,  155 

Maltase,  79 

Malt  amylase,  77 

Malt  sugar,  see  Maltose 

Maltose,  5,  10,  11,  86 

Manganese,  234 

Mango,  424 

Mangolds,  424 


446 


INDEX 


Mannans,  5,  i6 

Mannoheptose,  5 

Mannose,  5 

Manny,  average   weights   and    rates   of 

growth  of  children,  table,  372 
Manometer,  81 
Maple  syrup,  424,  430 
Marcuse,  value  of  phosphoproteins,  246 
Marmalade,  416 

Marshall,  comparative  value  of  organic 
and    inorganic    phosphorus,    252, 
258 
Masslow,   metaboUsm  of  organic  phos- 
phorus, 250 
phosphorus  for  growing  organism,  259 
Mastication,  191 

Mathews,  fats  and  lipoids  in  the  body,  35 
influence  of  mental  activity  on  metab- 
olism, 177 
lipins,  36,  40 

physiological  chemistry,  103,  137,  169, 
202,  283 
Means,  basal  metabolism  and  body  sur- 
face, 174,  202 
Means,    Aub,    and    DuBois,    effect    of 
caffeine  on  heat  production,  202 
Meat,  386,  387,  388,  389,  390,  391,  392, 

394,  397,  398,%424,  430 
Mechanical  efficiency  of  man,   181-185, 

200 
Meeh's    formula    for    computing    body 

surface,  172 
Meischer,    formation    of    organic    phos- 
phorus compounds,  246,  259 
Melezitose,  5 
MeUbiose,  5 

Meltzer,  advantage  of  high  protein  diet, 
378,  379 
calcium,  importance  of,  in  the  body, 

270 
factors  of  safety  in  animal  structure 
and  economy,  401 
Mendel,  abnormalities  of  growth,  357 
changes  in  food  supply  and  relation 

to  nutrition,  401 
gain  in  body  weight  of  children,  230 
nutrition  and  growth,  67,  233,  357 
viewpoints  in  study  of  growth,  357 
see  also  Osborne  and  Mendel 
Mendel  and  Daniels,  behavior  of  stained 
fats  in  body,  40 


Mendel  and  Judson,  changes  in  water, 
fat,  and  ash  content  of  body  dur- 
ing growth,  338,  339 
influence  of  different  types  of  stunting 

upon  body  composition,  342 
relations   between   diet,   growth,  and 
composition  of  the  body,  357 
Mendel  and  Osborne,  growth,  357;    see 

also  Osborne  and  Mendel 
Metabolism,  at  various  ages,  193-198 
basal,  1 51-168,  170-179 
behavior    of    foodstuffs    in,    104-137, 

138 
conditions  affecting,  170-233 
definition  of,  xi 
during  fasting,  188,  189,  200 
effect  of  muscular  work,  179,  180 
energy  requirement  in,  148-202 
fate  of  foodstuffs  in,  104-137 
.    in  disease,  178 

influence  of  age  and  growth,  193-198 
food,  188-191,  201,  202,  207-217 
muscular  work,  179-188,  226-229 
previously  stored  fat  and  glycogen, 

204-207 
size,  etc.,  170,  171,  174,  175 
temperature,  191-193 
thyroid,  178 
internal  activities,  and  secretions,  175, 

178 
mineral,    234-309 

calcium,  260-268,  272,  282-284 
iron,  285-309 
phosphorus,  242-259 
sulphur,  239-242 
protein,  1 18-137,  203-233,  374-382 
of  adults,  170-202 
of  growing  children,  196,  197 
purine,  130-134,  136-137 
Metaproteins,  53,  405 
Methyl  glyoxal,  105,  106,  107,  108,  109, 

115,  126,  216 
Methylpentoses,  4 
Metschnikoff,  intestinal  bacteria,  96 
Metschnikoff  and   Woolman,   intestinal 

putrefaction,  103 
Michaelis,    hydrogen  ion  concentration, 

283 
Milk,  146,  241,  256,  269,  289,  302^53, 
386,  387,  388,  389,  390,  391,  392, 
394,  397,  398,  416,  424,  430 


INDEX 


447 


Milk  sugar,  see  Lactose 

Millet,  425 

Millon  reaction,  71 

Mills,  injection  of  fatty  oils,  117 

Mince  meat,  417 

Mineral  elements,  see  Ash  constituents, 
also  Inorganic  elements 
function  of,  236 

Mineral  metabolism,  234-309 

Mitchell,  feeding  isolated  amino  acids,  67 

Molasses,  386,  387,  388,  389,  390,  391, 
392,  417,  42s,  430 

Molecular  weights  of  proteins,  50 

Monaminodicarboxylic  acids,  44 

Monaminomonocarboxylic  acids,  43 

Monosaccharides,   2,  4,   5,   6,   8,   17-18, 
79,  104 

Monosaccharoses,  4,  6-8,  17-18,  79,  104 

Moore  and  Bergin,  reaction  of  intestinal 
contents,  92 

MorguHs,  influence  of  feeding  on  metab- 
olism, 202 

Moro,  intestinal  bacteria,  96 

Moulton  and  Trowbridge,   composition 
of  beef  fat,  30,  40-41 

Mucilages,  5 

Mucins,  S3 

Mulder,  on  protein,  42 

Munk,  storage  of  food  fat  in  the  body,  32 

Murlin,    energy    requirement    in    preg- 
nancy, 199 
nutritive  value  of  gelatin,  233 
respiration    incubator    for    study    of 
energy  metaboUsm,  202 

Murlin  and  Bailey,  energy  requirement 
of  new-born,  195 
protein  metabolism  in  pregnancy,  233 

MurUn    and    Greer,    heart    action    and 
energy  requirement,  175 

Murlin  and  Hoobler,  metabolism  of  chil- 
dren, 202 

Murlin  and  Lusk,  influence  of  ingestion 
of  fat,  202 

Muscular  work,  179-188,  226-229 

Mushrooms,  417,  425 

Muskmelons,  417,  425,  430 

Mustard,  425 

Mutases,  76 

Mutton,  417,  425,  430 

Myosin,  49,  52,  240,  2^ 

Myri^c  add,  22,  116 


Nectarines,  417 
Nef,  behavior  of  sugars,  7,  17 
Nencki,  formation  of  fatty  acids,  114 
Nelson,   phosphorus  content  of   starch, 

13,  18 
Nelson   and    Vosburgh,    kinetics   of   in- 

vertase  action,  103 
Nelson   and  Williams,   calcium  output, 

264,  283 
Neimiann,  dietary  study,  150,  151 
Neutrality,  77,  273-284 
Nicotinic  acid,  327 
Nitrogen,  balance  experiments,  207,  208, 

209,  210,  215 
distribution  of  excreted,  135,  136 
fate  in  protein  metabolism,  128 
in  body,  234 
metabolism, '130 
see  also  Protein 
Northrup,  phosphorus  content  of  starch, 

13,  18 
Northrup    and    Nelson,    phosphorus    in 

starch,  244 
Nothnagel,  practical  medicine,  309 
Nucleic  acids,  130-137 
Nuclein,  131 

Nucleoalbumins,  see  Phosphoproteins 
Nucleoproteins,  53,  130,  131,  243,  405 
Nucleosides,  131,  132 
Nucleotidases,  131,  132 
Nucleotides,  132  ;  see  also  Nucleic  acid 
Nutritive  ratio,  147,  148 
Nutritive     requirements,     see     Energy, 

Food,  and   under   the   individual 

nutrients 
Nuts,  386,  387,  388,  389,  390,  391,  392, 

395 
Nuttall  and  Thierf elder,  intestinal  bac- 
teria, 95 

Oatmeal,   146,   241,   256,   269,  302,  394, 

417,  425,  430 
Octoic  acid,  113,  114 
(Edema,  324 

Ohler,  experimental  polyneuritis,  329 
Okra,  417,  425 
Oleic  acid,  23 
Olein,  23,  30 

Olives,  395,  417,  425,  430 
Olive  oil,  146,  394 
Onions,  395,  417,  425,  430 


448 


INDEX 


Oppenheimer,  enzymes,  103 

Oranges,   146,  256,   269,  302,  395,  417, 

42s,  430 
Ornithine,  44,  129 
Oryzanine,  324,  325 

Osborne,    chemical   nature   of   diastase, 
72,  73 

ratio  of  nitrogen  to  sulphur,  240 

plant  proteins,  60,  61,  68 

structure  of  proteins,  47,  49 

sulphur  in  proteins,  283 
Osborne    and    Mendel,    acceleration    of 
growth  after  retardation,  358 

amino  acids  in  nutrition  and  growth, 
358 

bacteria  in  feces,  103 

cottonseed  flour,  354 

efl&ciency  of  individual  proteins,  233 

experiments  with  isolated  food  sub- 
stances, 55-68,  224,  357 

experiments  with  restricted  amounts 
of  adequate  proteins,  340 

gliadin  in  nutrition,  358 

growth  upon  diets  of  isolated  food 
substances,  358 

growth-promoting  effect  of  protein- 
free  milk,  332 

influence  of  butter  fat  and  other  fats 
on  growth,  39,  358 

nutritive  factors  in  animal  tissues,  358 

nutritive  properties  of  proteins,  55- 
68,  224-226,  233,  339-342,  358 

problem  of  protein  minimum,  358 

relation  of  growth  to  chemical  con- 
stituents of  diet,  55-68,  224-226, 
233,  339-346,  358 

relative  efficiency  of  proteins,  55-68, 
225,  226,  358 

resumption  of  growth  after  long  con- 
tinued failure  to  grow,  358 

soy  bean  as  food,  358 

stability  of  growth-promoting  sub- 
stance of  butter  fat,  358 

suppression  of  growth,  57,  63,  64,  224, 

341 

vitamines,  r61e  of,  in  diet,  3  29 

zein  in  growth,  66,  224,  340 
Osborne,   Mendel,   and  Ferry,  effect  of 
retardation  of  growth  upon  breed- 
ing period  and  duration  of  life, 
•358 


Osborne,  Van  Slyke  et  al.,  products  of 

hydrolysis  of  proteins,  68 
Ovalbumin,  225 

OvovitelUn,  49,  53,  61,  225,  243,  246 
Oxidases,  75 
Oxygen,  234 

consumption,  181 
Oxyhemoglobin,  49,  50,  53 
Oxy proline,  61 
Oxy  purine,  132 
Oysters,  417,  425,  430 

Palmitic  acid,  22,  116 

Pancreatic  juice,  90,  91 

Paprika,  425 

Parsnips,  395,  417,  425,  430 

Passage  of  different  foods  through  the 
digestive  tract,  86,  87,  89,  92, 
93 

Paton,  formation  of  complex  phosphorus 
compounds,  246 

Pawlow,  digestion,  80,  87,  103 

Peaches,  146,  395,  417,  425,  430 

Peanuts,  146,  256,  269,  302,  395,  418, 
425,  430 

Pearl,  effect  of  feeding  pituitary  sub- 
stance and  corpus  luteum  on 
egg  production  and  growth,  359 

Pears,  395,  418,  425,  430 

Peas,  241,  302,  395,  418,  425,  430 

Pea  soup,  417 

Pecans,  395,  425,  430 

Pectins,  5,  17,  18 

Pekelharing,  pepsin,  71,  72 

Pentosans,  5,  11 

Pentoses,  4,  132 

Peppers,  418,  425,  430 

Pepsin,  71,  73,  77,  80 

Peptids,  45,  54,  406 

Peptones,  54,  59,  73,  406 

Perch,  430 

Peristalsis,  85,  90-94 

Persimmons,  418,  425,  430 

Petit,  pepsin,  78 

Pfliiger,  fat  formation,  127 
glycogen,  137 

PhaseoUn,  52,  60 

Phenol,  98 

Phenylalanine,  43,  45.  47,  60,  61,  125, 
126,  403 

Phlorizin  diabetes,  118,  124 


INDEX 


440 


Phosphates,  243-259,  276-283;  see  also 

Phosphorus 
Phosphatids,  37,  38-39,   243,   244,   246, 

322;  see  also  Phospholipins 
Phospholipins,  36,  38-39,  243,  244,  246, 

322 
Phosphoproteins,  243,  244,  246,  405 
Phosphoric  acid,  39,  131,  132,  243-248, 

276-283 
Phosphorus,  234,  271,  272,  383 

amounts  in  dietaries,    255,   256,   257, 

391-396 
amounts  in  food  materials,  256 
comparative    value    of    organic    and 

inorganic,  250,  252 
compounds,  classified,  243 
effect  of  deficiency,  343,  344 
excretion,  253 

metabolism,  242,  244,  254,  255 
requirement,  252,  253,  255,  383,  391- 
396 
Photosynthesis,  i,  2 
Phycetoleic  acid,  23 
Phytates,  244,  246 
Phytic  acid,  244 
Phytin,  322,  323 
Phytosterol,  37 
Phytosynthesis,  i,  2 
Pies,  418 
Pignolias,  418 

Pineapple,  146,  395,  4x8,  425,  430 
Pine  nuts,  418 
Pistachios,  418 
Pitcairn,  triturating  action  of  stomach, 

70 
Play  fair,  dietary  standard,  363 
Plimmer,  constitution  of  proteins,  68 
metabolism    of    organic    phosphorus 
.     compounds,  259 
Plums,  146,  395,  418,  42s,  430 
Polyneuritis,  318,  321,  327 
Polypeptids,  46,  54,  403 
Polysaccharides,  4,  5,  11-18 
Polysaccharoses,  4,  5,  11-18 
Pomegranates,  418,  426 
Pork,  418,  426,  430 
Portions,    Standard    or    loo-Calorie,    of 

foods,  144-146,  410-420 
Potassium,  234,  237,  271,  272 
Potatoes,   146,  241,  256^269,  302,  395, 
418,  426,  430 
2  G 


Pottevin,  reversion  of  enz5mie  action,  79 
Poultry,  386,  387,  388,  389,  390,  391,  392 
Prausnitz,    composition    of    feces    from 

different  diets,  99 
Primary  protein  derivative,  53,  405,  406 
Proline,  44,  47,  56,  60,  61,  126 
Protamins,  53,  404 
Proteans,  53,  405 
Proteases,  74,  75 
Proteid,  403 
Protein  (s),  42-68,  403 
absorption  of,  119 
acid-,  54 

alcohol-soluble,  404 
*alkali-,  54 

allowance,  376-380,  381 
classification,  51-54,  403-406 
coagulated,  54,  406 
complete,  224,  225 
composition  of,  48-50 
conjugated,  53,  405 
derivatives,  53,  54,  405-406 
derived,  53,  405 
energy  value  of ,  142,  143 
general  properties,  42-51 
hydrolysis  of,  46,  47,  118 
incomplete,  225,  340,  341 
injection  of,  1 20 

in  growth,  55-68,  339-340.  355-358 
in  neutrality,  278 
metabolism,    1 18-137,    203-233,    339- 

342,  373-382 
in  fasting,  203,  204 
influence  of  body  fat,  205,  206 
molecular  weights,  50 
opinions  upon  liberal  diet,  374,  375, 

376,  377 
partially  incomplete,  225 
primary  derivatives,  53,  405 
properties,  of  individual,  54-67 

physical,  51 
putrefaction  of,  97 

requirement,   217-220,  339-340,  373- 
382,  383 
determining  factors,  203 
effect  of  muscular  exercise,  227 
influence  of  choice  of  food,  222,  223 
relation   to   age   and   growth,    229, 

230,  231 
results  of  experiments,  220 
versus  protein  standard,  220-222 


450 


INDEX 


Protein  (s)  —  Conlinued 

respiratory  quotient,  no,  in 

secondary  derivatives,  406 

simple,  52,  403,  404 

sparing,  210-217 

standard,    220-222,    273,    274,    373- 
382,  383 
for  children,  381,  382-383 
for  families,  382-383 

utilization  in  tissues,  122,  123 

value  of  high  intake,  375,  378,  379 
Proteolytic  enzyme,  see  Proteases 
Proteoses,  54,  59,  73,  406 
Prunes,    146,    256,    269,   302,   395,   419, 

426,  430 
Psychic  factors  in  digestion,  80-83,  88 
Ptyalin,  73,  76,  79,  83,  86 
Pumpkins,  419,  426,  430 
Purines,  130,  131,  327 
Putrefaction,    98 
Putrefactive  bacteria,  97,  98 
Pylorus,  83,  84,  85,  86 
Pyridines,  326,  327 
Pyrimidines,  131,  133,  323,  327 
Pyruvic  acid,  108,  109,  114,  125,  216 
Pyruvic    aldehyde,    124,    125;    see    also 
Methyl  glyoxal 

Radishes,  395,  419,  426,  430 

Raffinose,  5 

Raisins,  146,  395,  419,  426,  430 

Raper,  normal  octoic  acid,  114 

Raspberries,  419,  426,  430 

Rate  of  passage  of  foods  through  the 

digestive  tract,  86,  87,  89,  92,  93 
Reaumur,  gastric  digestion,  70 
Reductases,  75 
Regulation  of  body  temperature,    191- 

193 
Reichert,   differentiation  and  specificity 

of  starches,  12,  18 
Relation  of  height  and  weight,  367-370, 

372,  373 
Rennin,  75,  78 
Requirements,   see  Food  Requirements; 

see  also  Metabolism;    also  Stand- 
ard 
Resorption,  93 
Respiration   experiments,   151;   see   also 

Calorimeter 
work  of,  168 


Respiratory    quotient,    109,    no,    in, 
152,  153,  154,  187 

Rettger,   influence   of   milk   feeding   on 
mortality  and  growth,  359 

Ribose,  4,  132 

Rice,  146,  256,  269,  302,  350,  394,  419, 
426,  430 
protein,  products  of  hydrolysis,  ref.,  68 

Richardson  (A.  E.),  and  Green,  cotton- 
seed flour,  353,  359 

Richardson  (W.  D.),  chemical  character- 
istics of  lard,  41 

Riche,  adiabatic  bomb  calorimeter,  140 

Rhamnose,  4 

Rhubarb,  419,  426,  430 

Robertson,  chemical    mechanism    main- 
taining neutrality,  283 
growth,    and   growth-controlling   sub- 
stances of  pituitary  body,  359 

Roentgen  rays,  84,  86,  92,  93 

Rohmann,    phosphoproteins    versus    in- 
organic phosphates,  247 

Romaine  (salad),  426 

Rona,  absorption  of  amino  acids,  120 

Rose,  creatinuria,  137 

Rose  and  Cooper,  potato  nitrogen,  224, 
233 

Rubner,  energy  metabolism,  169,  170 
fuel  values  of  food  constituents,  143 
influence  of  food  on  metabolism,  189, 

190 
relation  of  body  surface   to   metabo- 
lism, 171 
specific  dynamic  action  of  foodstuffs, 
189-190 

Rubner  and  Heubner,   storage  of  food 
for  growth,  194 

Rutabagas,  426,  430 

Rye,  426,  430 

Saccharose,  see  Sucrose 
Salivary  digestion,  80,  82-84 
Salmon,  146,  419,  426,  430 
Salt,  craving  for,  237-239 

effect  upon  metabolism,  239 
Saponification,  19 
Sapota,  426 
Sausage,  419 
Scallop,  61 

Schaumann,  beriberi,  322,  329 
Schlossmann,  phosphorus  in  milk,  259 


INDEX 


Z> 


451 


Schondorflf,  distribution  of  glycogen  in 
the  body,  15 

Schmidt,  medicinal  iron  in  hemoglobin 
formation,  296 

Schmidt  and  Strassburger,  composition 
of  feces;    ref.  103 

Schottelius,  bacterial  action  in  digest 
95.  q6 

Schryver  and  Haynes,  pectins,  18 

Schulze  and  Reineke,  composition  of 
fat  of  different  mammals,  30 

Schwann,  pepsin,  71 

Score  value,  392-395 

Scurvy,  310-318,  327-329 

Secalose,  5 

Secondary  protein  derivatives,  54 

Secretin,  91,  92 

Sedoheptose,  5 

Seeds,  deficiency  as  sole  food,  352,  353 

Seegen,  formation  of  carbohydrate  from 
protein,  123 

Seidell,  antineuritic  vitamine,  325,  329 

Serine,  43,  45,  47,  60,  61,  126 

Serum  globulin,  49,  52,  240 

Sex,  relation  to  food  requirement,  199, 
264-265,  300,  371,  372 

Shad,  419 

Shaflfer,  nitrogen  output  during  rest  and 
work,  229 

Sherman,  iron  in  food  and  nutrition, 
298-309 

Sherman  and  Baker,  starch,  13,  18 

Sherman  and  Gettler,  balance  of  acid- 
forming    and    base-forming    ele- 
ments, 279-280,  283 
chemical  nature  of   enzyme  prepara- 
tions, 103 

Sherman  and  Gillett,  adequacy  and 
economy  of  city  dietaries,  401 

Sherman,  Mettler  and  Sinclair,  calcium, 
magnesium,  and  phosphorus  in 
food  and  nutrition,  259 

Sherman  and  Schlesinger,  pancreatic 
amylase  preparation,  78,  103 

Shredded  wheat,  419,  426,  430 

Shrimp,  426 

Silicon,  234 

Sitosterol,  37 

Siven,  protein  requirement,  233 

Size,  relation  to  metabolism,  170-175; 
see  also  Age;    Children 


Sjostrom,   influence  of  temperature  on 

carbon  dioxide  output,  202 
Skatol,  98 
Skraup  and  Behler,   structure  of  gelp^/ 

,  ;^"^  AT---^^.^  ^^^ 

/  ^Bgidlev.  formation  of  fat  from    carbo- 
t4«tv  hydrate,  41,  114,   115 

Snell,  bomb  calorimeter,  139 
Socin,    experiments    with    organic    and 

inorganic  iron,  288,  309 
Soderstrom,  Meyer,  and  DuBois,  com- 
parison   of    metabolism    of    men 
flat  in  bed  and  sitting  in  steamer 
chair,  202 
Sodium,  234,  271,  272 
Soluble  starch,  14 

Sonden  and  Tigerstedt,  energy  metabo- 
lism, 157 
Sorbose,  5 
Sorensen,    hydrogen   ion   concentration, 

77 
Soup,  426 

Spallanzani,  gastric  juice,  70,  71 
Specific   dynamic   action   of   foodstufi^s, 

189-191,  201,  202 
Spinach,  146,  302,  395,  419,  426,  430 
Squash,  395,  419,  426,  430 
Stachyase,  5 

Standards,  dietary,  361-367,   382,    383, 
385 
for  calcium,  267,  382,  383 
for  energy,    183,    186,    187,    196-197, 

360-373 
for  iron,  299-300,  382,  383 
for  phosphorus,  255,  382,  383 
for  protein,    220-222,    229-233,   373- 
383,  385 
Starch,  5,  12-14,  i7.  18,  73,  83,  142 
Starch  sugar,  see  Glucose 
Starling,  hormones,  88,  89 
physiology  of  digestion,  103 
secretion  of  bile,  91 
Steapsin,  90 

Stearic  acid,  22,  116,  216 
Stearin,  216 

Steenbock  and   Hart,    calcium    require- 
ment of  animals,  265,  284 
Steenbock,  Nelson,  and  Hart,  acidosis, 

284 
Steinitz,  phosphoproteins,  246 
Stepp,  Hpoids,  39-40 


452 


INDEX 


Sterols,  36,  37-38 

Stevens,  experiments  with  gastric  juice, 

70 
Stockman,  absorption  of  inorganic  iron, 
289,  290 
iron  requirement,  298 
Stoeltzner,    significance   of    calcium    in 

growth  of  bone,  284 
Stoklasa,     iron-protein     compound     of 

onion,  306 
Stomach,  82-89 
Strawberries,  419,  426,  430 
Substrate,  76 

Sued,  metabolism  during  fasting,  206 
Succotash,  419 
Succus  entericus,  89 
Sucrase,  77,  79,  92,  103    * 
Sucrose,  5,  8yio,  14*2  ^       ^    ^     ** 

Sugar,  2,  146,  ^86,*  387,  388,  389,^  390, 
39i>  *392,   394,  419;  see  also  Su- 
crose 
double,  4 
references,  17,  18 
simple,  2 
Sulpholipins,  36 
Sulphur,  234-242,  271,  272 
elimination,  242 
metabolism,  239,  240,  241 
proportion  in  protein,  49,  240,  241 
Suzuki,  Shamimura,  and  Odake,  oryza- 

nine,  329 
Swartz,  utilization  of  cellulose,  16,  18 
galactans,  17,  18 
mannans,  16,  18 
pentosans,  11,  18 
Sylvius,  fermentation  and  digestion,  69 
Symonds,  tables  of  heights  and  weights, 

368 
Syntonin,  54 

Tagatose,  5 

Takaki,  beriberi,  319 

Talbot,  energy  requirement  of  infants, 

202 
Tallquist,   protein-protecting  powers  of 

fat  and  carbohydrate,  212-214 
Talose,  5 
Tamarind,  426 
Tangl,  metabolism  of  an  artificially  fed 

child,  284 
Tapioca,  426,  430 


Tartakowsky,  assimilation  of  inorganic 

iron,  29s,  309 
Tashiro,   carbon   dioxide   production  in 

nerve,  177,  202 
Taylor,    diet    of    prisoners    of    war   in 
Germany,  401 

digestion  and  metabolism,  103 

fats  and  lipoids  in  body,  35 
Temperature,  see  Regulation 
Terminolo^ToT  hydroly tic  enzymes,  76 
Tetrahexoses,  5 
Tetranucleotides,  131 
Tetrasaccharides,  5 
Tetrasaccharoses,  ."; 
Tetroses,  4 

Thioamino  acid,  see  Cystine 
Thomas  (A.  W.),  constitution  of  starch, 
13,  18 

phosphorus  content  of  starch,  13,  18 
Thomas    (K.),    nutritive    eflBciency    of 

proteins,  223 
Threose,  4 

Thrombin  or  thrombase,  75 
Thymine,  131,  132,  133 
Thsnnonucleic  acid,  53 
Thymus,  132 
Thyroid,  178 

Tigerstedt,     ash    content    of    ordinary 
dietary,  284 

estimates  of  food  requirements,   186, 
187 

metabolism  at  various  ages,  194 

metaboUsm  during  fasting,  189 
Tomatoes,  146,  395,  419,  426,  430 
Toruline,  324,  325 
Transportation,  effect  upon  prices,  398, 

399 
Trehalose,  5 

Triglycerides,  simple  and  mixed,  24-27 
TrigoneUine,  327 
Trihexoses,  5 
Triolein,  79 
Trioses,  4 
Trioxypurine,  132 
Tripeptids,  46 
Trisaccharides,  5 
Trisaccharoses,  5 
Triticonucleic  acid,  53 
Truffles,  426 
Trypsin,  77,  80,  90,  92 
Trypsinogen,  92 


INDEX 


453 


Tryptophane,  44,  45,  47,  48,  60,  61,  62, 
63,  71,  120,  127,  224,  339,  341 

Tuberin,  52 

Tubular  glands,  91 

Tuna,  419 

Turanose,  5 

Turkey,  419 

Turnips,  146,  256,  269,  302,  395,  420, 
426,  430 

Tyrosine,  43,  45,  47,  60,  61,  125 

Underbill,    metabolism    of    ammonium 

salts,  137,  284 
Uracil,  131,  132,  133 
Urea,  129,  142 
Uric  acid,  130-134,  281 
Urico  lysis,  134 
Uridine,  132 
Uridine  nucleotide,  132 
Urine,  acidity,  281 

Valine,  43,  47,  48,  60,  61,  120,  126 

Van  Slyke,  amino  acids  in  intermediary 
metabolism,  1 19-122 
amino  acids  in  physiology  and  pathol- 
ogy, 137 

Van  Slyke  et  al.,  fate  of  protein  digestion 
products,  1 19-122,  137 

Van  Slyke,  CuUen,  Stillman,  and  Fitz, 
acid  excretion  and  alkaline  re- 
serve, 284 

Van  Slyke  and  Meyer,  absorption  and 
distribution  of  amino  acids,  119- 
120 

Von  Helmont,  digestion,  69 

Von  Hosslin,  relation  of  size  to  heat 
production,  171 

Von  Noorden,  metabolism  dependent 
upon  build  of  body,  174 
metabolism  and  medicine,  169,  202,  233 
need  for  high  protein  intake,  375,  376 
nitrogen  equilibrium,  207-210 
use  of  vegetables  in  feeding  children, 
308 

Von  Wendt,  dicalcium  phosphate,   247, 
309 
iron  requirements,  298,  309 

Veal,  420,  427,  430 

Vedder,  beriberi,  330 

Vegetables,  386,  387,  38^  389,  39o,  391, 
392,  394,  397,  398 


Vegetable  soup,  420 

Venous  radicles,  90 

Vernon,  intracellular  enzymes,   103 

Vicihn,  60 

Vignin,  52,  60 

Vinegar,  427,  430 

Vitamines,  xii,  323,  324,  325,  345 

Voegtlin,  vitamines,  330 

Voegtlin  and  White,  can  adenine  acquire 
antineuritic  properties,  330 

Voit,  calcium  in  animal  nutrition,  284 
dietary  standard,  362 
effects  of  insufficient  calcium,  262 
fat  production  from  protein,  127 
food  requirement,  180,  362 
iron  metabolism  in  dogs,  288,  289 
nitrogen  elimination  in  fasting,  204 
phosphorus   metabolism    during   fast- 
ing, 253 

Walnuts,   256,  269,  302,  395,  420,  427, 

430 
Water  cress,  427,  430 
Watermelon,  420,  427,  430 
Waters,    capacity    of   animals   to   grow 

under  adverse  conditions,   359 
experiments      with      energy-deficient 

diets,  336,  337  , 
influence  of  nutrition  on  animal  form, 

359 
Water   soluble   B,    xiii,   333,   345,    347, 

383,  384,  see  also  Growth 
Waxes,  36 
Weight,  relation  to  height  and  age,  197, 

368,  369,  371,  372 
Wells,  nucleoproteins,  131 
Wheat,  146,  241^  256,  269,  302,  420,  427, 

430 
embryo,  349,  35° 
kernel,  349 
Whey,  427,  430 
White  bean,  351,  352 
Whitefish,  420 
Whortleberries,  427,  430 
Willcock  and  Hopkins,   feeding  exjjeri- 

ments  with  zein  and  amino  acids, 

55 
Williams,  chemical  nature  of  vitamines, 

330 
relation  of  chemical  structure  to  anti- 
neuritic action,  326,  327 


454 


INDEX 


Williams    and    Saleeby,    treatment    of 

human  beriberi,  330 
vitamine  preparation,  325 
Williams  and  Seidell,  vitamine  of  yeast, 

327 
Wilson,     nitrogen     metabolism     during 

pregnancy,  233 
Wine,  427,  430 

Withers  and  Carruth,  gossypol,  353 
Wolffberg,   formation    of    carbohydrate 

from  protein,  123 
Woltering,    experiments   with   inorganic 

iron,  290,  309 
Woodyatt,     carbohydrate     metabolism, 

137 
Work,    influence   on    metabolism,    179- 

188,  226-229 
Wright,  scurvy,  313 

Xanthine,  132,  133 
Xanthoprotein  test,  71 
Xylans,  5 


Xyloketose,  4 
Xylose,  4 

Yeast,  75,  132 
Yoshikawa,    Yana, 
beri,  330 


and    Menals,    beri- 


Zadik,  phosphoproteins,  246 

Zein,  47,  48,  49,  so,  52,  55,  57,  61,  65, 

6s,  66,  224,  22s,  240,  339 
Zuntz,     metabolism     experiment     with 

ergometer,  185 
respiration  mask,  isi 
work,    and   consumption    of    oxygen, 

181 
Zuntz  and  Morgulis,  influence  of  under 

nutrition  on  metabolism,   202 
Zuntz  and   Schumberg,   energy   values, 

153 
Zwieback,  420 
Zymase  of  yeast,  75 
Zymogen,  76 


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